Evolution and Biodiversity

Category: parental care (Page 2 of 3)

Scattering sand

Sea turtle creates decoy nests on the beach

sea turtle creates decoy nests

Sea turtle eggs, buried in a sandy beach, are an attractive meal for some animals. Turtle mothers confuse these enemies with a series of decoy nests, Thomas Burns and colleagues think.

For a sea turtle female, it is physically demanding to lay her eggs. She crawls from the sea onto a sandy beach, selects a suitable place, digs a hole, lays dozens of eggs in it and refills the nest cavity. You would expect her to return to the sea as soon as possible, where she can move more easily and is safer.

But she doesn’t, as Thomas Burns and colleagues report. She first scatters sand around the refilled egg chamber. And then she starts to travel a convoluted path over a large area, further and further away from the nest, stopping periodically to scatter sand again. Only after having done this at several scattering stations, she will leave the beach. What is this extra effort good for?

Tasty

Sea turtles lay their eggs on tropical and subtropical beaches worldwide; afterwards, they don’t look after their clutches any more. The eggs develop in the warm sand, and the young turtles dig through the sand and crawl to the sea. All a mother can do for her offspring is to make sure not to betray the location of the nest, where she has dug in the sand, to predators. The tasty eggs are liked by various animals, including gulls, foxes, raccoons and wild pigs.

Biologists presumed that sea turtles scatter sand around their nests to disguise or camouflage them, so they won’t be noticed. But that can’t be the reason, Burns and colleagues argue after thoroughly studying the behaviour of leatherback sea turtle (Dermochelys coriacea) and hawksbill sea turtle (Eretmochelys imbricata). Because why, in that case, would sea turtles scatter sand also in places that are at considerable distance from the nest?

Big effort

The researchers, who worked on the islands of Trinidad and Tobago, point out that female sea turtles behave according to a fixed pattern until they have finished the nest. Thereafter, their movements become unpredictable. They take a random route on the beach, changing direction at each station.

Research also shows that scattering sand is a time-consuming and exhausting activity. The hawksbill sea turtle puts in as much energy as it does in excavating a nest hole and refilling it, and for the leatherback it is even the most strenuous activity. The hawksbill often scatters sand at more than ten stations, the leatherback may stop more than twenty times. Despite the great effort, the turtles persist: at the last stop they are as active as at the first.

The researchers’ conclusion: the sea turtles create a series of decoy nests. An natural enemy looking for eggs will mostly dig in vain and lose a lot of time. As a consequence, real nests are less easily found and therefore safer.

Willy van Strien

Photo: Eretmochelys imbricata. Gerwin Sturm (Wikimedia Commons, Creative Commons CC BY-SA 2.0)

Sources:
Burns, T.J., R.R. Thomson, R.A. McLaren, J. Rawlinson, E. McMillan, H. Davidson & M.W. Kennedy, 2020. Buried treasure—marine turtles do not ‘disguise’ or ‘camouflage’ their nests but avoid them and create a decoy trail. Royal Society Open Science 7: 200327. Doi: 10.1098/rsos.200327
Burns, T.J., H. Davidson & M.W. Kennedy, 2016. Large-scale investment in the excavation and ‘camouflaging’ phases by nesting leatherback turtles (Dermochelys coriacea). Canadian Journal of Zoology. Doi: 10.1139/cjz-2015-0240

American coot takes care of the small

The younger, the brighter, the more food

Coot chicks' ornaments tell parents what age they are

In contrast to their parents, young coots have a striking appearance. Bruce Lyon and Daizaburo Shizuko discovered how their ornamentation helps the parents to optimally feed the offspring.

Young American coots, Fulica americana, have fancy heads: a red beak and bare patches of red skin with papillae, surrounded by a crown of orange-yellow modified feathers. That ornamentation is puzzling; because of predators, you would rather expect young coots to be unobtrusive. Bruce Lyon and Daizaburo Shizuko figured out what function their colourful appearance serves.

Starvation

If the clutch of a pair of American coots is complete, it is certain that not every egg will result in an independent young. The water birds lay nine eggs per nest on average, and although almost all of these eggs will hatch, only three or four young eventually reach independency. Four chicks is the maximum that the parents can feed. As a consequence, less than half of the chicks can survive.

The case is settled during the first ten days after the last egg has hatched. The young coots leave the nest immediately after hatching and swim to the parents to be fed, every chick trying to get attention. It is an unfair competition, because the siblings do not hatch at the same time; the first chick may be eleven days older than the last. The oldest chicks are larger, not only because they are older, but also because the first eggs laid by a female are larger. It is easy for them to keep up with their parents, while the youngest coots run a high risk of being too slow and starving.

The parents don’t interfere with this rivalry between their young.

Favourites

But after ten days, things will change, as the researchers had discovered before during their research in Canada. The size of the coot family then is reduced to a number that the parents can handle, and they shift strategies. They are now going to pay attention to the small ones and offer them most of the food that is available. Each parent chooses one of the chicks to favour; a favourite is always one of the youngest.

The eldest chicks also want to be fed, but they are already able to find their own food. They are tousled by their parents when they come begging: they are grasped by the neck and shaken. They then will give up.

In this way, the parents give full attention to the chicks that need it, making sure that all chicks that survived the period of sibling rivalry can grow up. Thanks to this preferential treatment, the youngest chicks in a coot family will gain the same weight as the oldest ones.

Age

The researchers also had observed earlier that the most brightly coloured young were preferentially fed by the parents and more likely to be chosen as a favourite. Now, they link the chicks’ colour to their age. The later an egg’s position in the laying order, they show, the brighter coloured the chick will be. This is probably because the mother adds more dye to the yolk as she has already laid more eggs. So this appears to be the function of the ornamentation: it indicates to the parents which chicks are the youngest and need food aid the most.

Sometimes a coot is extremely aggressive to a chick. In that case, this is not its own young, but another coot’s. Coot females often dump an egg in the neighbours’ nest in an attempt to increase the breeding success. But the intended foster parents recognize such foreign chick and will tackle it hard. Its chance to survive is very small.

Willy van Strien

Photo: American coot with chicks. M. Baird (Wikimedia Commons, Creative Commons CC BY 2.0)

Sources:
Lyon, B.E. & D. Shizuka, 2019. Extreme offspring ornamentation in American coots is favored by selection within families, not benefits to conspecific brood parasites. PNAS, online Dec 30. Doi: 10.1073/pnas.1913615117
Shizuka, D. & B.E. Lyon, 2013. Family dynamics through time: brood reduction followed by parental compensation with aggression and favoritism. Ecology Letters 16: 315-322. Doi: 10.1111/ele.12040
Lyon, B.E., 1993. Conspecific brood parasitism as a flexible female reproductive tactic in American coots. Animal Behaviour 46: 911-928. Doi: 10.1006/anbe.1993.1273

Costs before benefits

By guarding stepkids, bee male may get the mother

In bee Ceratina nigrolabiata, the male takes care of other males' offspring

Ceratina nigrolabiata bee males guard the nest of their female partner. This seems surprising, as the brood consists mainly of other males’ offspring, as Michael Mikás and colleagues show. Still, the males have good reason.

Bee males don’t do much. Okay, they mate with females and of course that is important, but that’s it. The females construct a nest and take care of the offspring. In solitary species, such as the species that visit a bee hotel, each female makes her own nest; social species, such as the honeybee, live in groups in which queens produce eggs and workers do the work.

There is one exception, Michael Mikát and colleagues report: in the solitary bee species Ceratina nigrolabiata, males do participate in care – but, surprisingly, mainly by protecting other males’ offspring.

Guard

A Ceratina nigrolabiata female makes her nest in the hollow stem of a plant. She goes inside, lays an egg, brings food for the larva that will hatch, closes the space by building a wall and lays another egg in the next part of the stem. Ultimately, a nest consists of six to seven cells in a row, with young in a descending stage of development when viewed from the inside out. The mother leaves when the nest is completely provisioned.

In the majority of nests in which a female is active, a male is present, as the researchers observed during their studies in the Czech Republic. When the female performs foraging trips, the male stays inside the nest to protect it from predators such as ants, driving them away when they come near. He is sitting near the entrance with the head facing inwards. When she returns, she will scratch his abdomen and he will let her pass.

The benefit for her is clear: thanks to this guard, she can leave to forage without having her nest unattended.

For him, it is different. DNA analyzes show that in most cases the brood that he protects does not contain any offspring that he fathers. So he takes care of other males’ offspring, and in general, that is not a good strategy from an evolutionary point of view.

Male switches

In fact, the bee males have no interest in the brood at all; it is the mother that captivates them. A male only has a chance to mate if he finds a female and stays with her until she is willing; in Ceratina nigrolabiata, a female will mate several times in her life. So he has to stay at her nest. While he certainly participates in care by actively protecting the brood, this stepfather care is a by-product of monopolizing a female, according to the researchers.

And indeed, if they removed a female from her nest, the male abandoned the brood.

So, every female is assured of a helpful lover. If a male disappears, his place is usually taken by another.

These stepfathers are not ideal helpers, because they stay on average for only seven days, while a female needs about forty days to complete her nest. As a consequence, the male inhabitant of most nests changes one or more times, and in fatherless periods the female spends less time collecting food, staying on the nest instead. The more changes, the fewer offspring she therefore can produce. But at least she gets help, which is unique among solitary bees.

Willy van Strien

Photo: Ceratina nigrolabiata, female returns at her nest in a hollow plant stem and scratches the guarding male. ©Lukáš Janošík

Source:
Mikát, M., L. Janošík, K. Cerná, E. Matoušková, J. Hadrava, V. Bureš & J. Straka, 2019. Polyandrous bee provides extended offspring care biparentally as an alternative to monandry based eusociality. PNAS: 116: 6238-6243. Doi: 10.1073/pnas.1810092116

Care for everyone

Earwig mother tends foreign eggs and adopts orphans

earwig female cares for another female's offspring 

An earwig mother will treat another female’s eggs as caring as her own eggs, Sophie Van Meyel and colleagues write. Previously, Janine Wong and Mathias Kölliker had discovered that she is willing to accept young orphans in her family.

Earwigs are not very popular animals, but actually they are lovely creatures. The extensive and complex care that females provide to their offspring is impressive.

In late autumn, a female European earwig, Forficula auricularia, lays twenty to forty eggs in a burrow. She then remains in that nest and tends her clutch during winter. And that pays off: without her presence, almost all eggs would be lost, Sophie Van Meyel and colleagues show. A mother cleans the eggs with her mandibles to prevent growth of fungi and pathogens. She protects her clutch against predators. She ensures that the eggs will not desiccate. And she relocates them if necessary.

This nice maternal behaviour is not directed exclusively to a mother’s own clutch.

Weight loss

When the clutch of an earwig female is replaced by that of another female, she provides the same care with the same dedication, as Van Meyel witnessed when she conducted cross-fostering tests in the lab with five-day-old clutches. The eggs have their mother’s odour, so a female should be able to recognize foreign eggs. But she does not reject them. When tending eggs, a female faces a tough task, because she will not leave to forage until the young have hatched, which takes a few months. So, she will lose weight.

But strangely enough, the weight loss during winter is even greater for a female that has no eggs to tend. Apparently, food is scarce outside. A tending mother probably cannibalizes  some of her eggs to survive. This may explain that she is willing to care for a foreign clutch as well as for her own clutch, as the possession of eggs is a guarantee that she does not have to starve. She will be forgiven for consuming a small part of the clutch, since without her care almost no egg would make it through the winter months.

Orphans

The young hatch in early spring. Earwigs do not go through a complete metamorphosis with larval and pupal stages, but the juveniles resemble adult animals. They are nymphs.

After hatching, the nymphs usually stay in their burrow for a week. The mother protects them, regurgitates food for them and accompanies them when foraging at night. The nymphs can do without that care; they are mobile shortly after hatching and can search for food independently. But they do better if their mother attends them during the first week.

However, not every mother survives until spring, so some nymphs are orphans from the start of their life. Many such nymphs leave their natal nest during the first night. If they survive, they often join another family. Then again something remarkable happens: the mother of that family typically accepts them, and most orphaned nymphs end up well, as Janine Wong and Mathias Kölliker have shown.

Most motherless nymphs appear to choose an adoptive family with smaller juveniles. They are safe there, because when food is scarce, nymphs may cannibalize each other, preferring nonsibling smaller nymphs. By accepting foreign nymphs, an earwig family therefore runs a certain risk. Apparently,  group augmentation confers an advantage to the adoptive family that outweighs that risk, but it is not clear yet what that advantage might be.

Willy van Strien

Photo: European earwig female with eggs. ©Joël Meunier

Watch an earwig mother tending her eggs on You Tube

Sources:
Van Meyel, S., S. Devers & J. Meunier, 2019. Love them all: mothers provide care to foreign eggs in the European earwig Forficula auricularia. Behavioral Ecology, online 9 February. Doi: 10.1093/beheco/arz012
Wong, J.W.Y. & M. Kölliker M., 2013. The more the merrier? Condition-dependent brood mixing in earwigs. Animal Behaviour 86: 845-850. Doi: 10.1016/j.anbehav.2013.07.027

Curbed pregnancy

Pipefish father responds to sight of attractive female

male pipefish curb their pregnancy upon seeing an attractive female

A pipefish father with a filled brood pouch may see a female who produces better offspring than the mother of the embryos he currently carries. He will then curb his pregnancy, as Mário Cunha and colleagues show.

In pipefish, long thin fish species with a tubular snout, parental care is provided by the males. The fathers carry the fertilized eggs until the young hatch and swim away. In some species, including the black-striped pipefish (Syngnathus abaster), they even have a brood pouch, within which the water is of good quality and the eggs are protected and provided with oxygen and nutrients. Black-striped pipefish males carry eggs from three females per ‘pregnancy’ on average. They prefer to receive eggs of large partners, because then the pregnancy will result in more and larger offspring.

Now, a dilemma arises if a pregnant male encounters a female that is larger than the females whose eggs he is brooding, Mário Cunha and colleagues realized. A pregnancy that would yield more than the current one is within reach, but his pouch is already occupied. What would he do: just continue the pregnancy? Or would he break it off, end it earlier or invest less in it to save time and energy for a next brood?

Extremely attractive

To find out, the researchers brought pipefish into the lab and conducted experiments. They paired a number of males with one female of large size and waited until the embryos were developing. They then removed the mother and introduced a very large, extremely attractive female to some of the males. She was behind a transparant divider; the males could see and smell her, but physical contact was not possible.

The researchers checked how long the pregnancy lasted and measured the length of the young fish after birth. For comparison, other fathers were either allowed to remain in contact with the mother or exposed to another female that was equally sized.

embryo of pipefish Syngnathus abasterFathers who perceived a particularly large female were found to respond to this encounter. They curbed their pregnancy: its duration was shorter than that of other fathers, and the young fish that emerged were smaller. Another trial showed that it was more likely that some embryos died. So, when a male sees a very attractive partner, he will invest less in his current pregnancy.

Insensitive behaviour

In our view, that is insensitive behaviour. But it may occur if it increases the breeding success of pipefish fathers. In that case, a fast new pregnancy with high yield should compensate for the smaller number of offspring from the current pregnancy.

Willy van Strien

Photos:
Large: Syngnathus abaster. Giacomo Radi (Wikimedia Commons, GNU Free Documantation License 1.2)
Small: embryo of Syngnathus abaster near the end of the pregnancy. © Sara Mendes

Source:
Cunha, M., A. Berglund, S. Mendes & N. Monteiro, 2018. The ‘Woman in Red’ effect: pipefish males curb pregnancies at the sight of an attractive female. Proceedings of the Royal Society B 285: 20181335. Doi: 10.1098 / rspb.2018.1335

Why dad leaves his family

Conflict between moult and care in Hooded Warbler

When a Hooded Warbler male initiates moulting while still having dependent young, he often deserts

When parental care and feather replacement overlap in time, a Hooded Warbler male may abandon his family, forcing his mate to provide all remaining care for the young. The mother can handle it, as Ronald Mumme points out.

Migratory birds are under time pressure during the breeding season. Not only do they have to raise young, they also have to replace their feathers and store fat reserves to prepare for fall migration to their wintering area. Those tasks – caring, moulting and storing fat – may be in conflict.

The Hooded Warbler, which spends the summer in North America, has a very hard time, Ronald Mumme notices. Couples produce two clutches per season. The female incubates the eggs and when the young have hatched, both parents will provision them. The parents have to perform this job for about four weeks, for only then the young are independent. Hooded Warblers feed on winged insects, especially flies and mosquitoes, which they pick from the air. Before the young of the second clutch reach independency, it may already be time for the parents to initiate moult.

Indispensable tail

The problem now is that Hooded Warblers use their tail as foraging tool. The outer tail feathers have white spots that become visible when a bird spreads the feathers and that stand out against the olive-green background. By flicking its tail, a bird flushes flying insects hidden in the vegetation and captures them in the air.

But during moult, those feathers are shed simultaneously and a bird has to spend a week without a tail. It then has difficulty capturing insects, while it needs extra food because the moult is energetically demanding. And so it may happen that one of the parents leaves the family because it cannot obtain sufficient food for itself and the chicks, especially if they are so young that they cannot catch any food for themselves. Mostly, the father deserts, because males initiate moult on average two weeks earlier than females. Young, inexperienced fathers are more likely to leave than older dads.

Why males initiate moult earlier than females is not known yet.

Abandoned females

When the father deserts at the end of the season, the mother is left responsible for all remaining parental care. But apparently, she has no big problems: the chance that such a female survives the winter does not seem to decrease; the birds spend wintertime along the Caribbean coast of Central America. And in the next breeding season, she probably will choose the same mate, even though he had left her.

Willy van Strien

Photo: A male Hooded Warbler delivers food to his nestlings © Ron Mumme

Sources:
Mumme, R.L., 2018. The trade-off between molt and parental care in Hooded Warblers: simultaneous rectrix molt and uniparental desertion of late-season young. The Auk 135: 427-438. Doi: 10.1642/AUK-17-240.1
Mumme, R.L., 2014. White tail spots and tail-flicking behavior enhance foraging performance in the Hooded Warbler. The Auk 131: 141-149. Doi: 10.1642/AUK-13-199.1

Inequality

Red-capped plover invests more in young of opposite sex

male red-capped plover will provide more parental care to daughters

Fathers care more when they have daughters, mothers care more when they have sons. Such is the case in the red-capped plover, in which both parents divide the tasks of raising their two chicks, as Daniel Lees and colleagues witnessed.

In the red-capped plover, a bird that inhabits coastal areas of Australia, parents divide the care for their young. The nest is a shallow scrape on the ground wherein the female usually lays two eggs, open and exposed. The eggs are well camouflaged thanks to their yellowish-brown colour and black spots. They have to be, otherwise they would be easily detected during daytime by visually-foraging predators, such as the little raven. The female also has a protective coloration. But the male has a bright red head to impress females and help him acquire a high-quality mate. When he would incubate the eggs, his ornamentation would disclose their presence to predators.

Red fox

In order to prevent this from happening, the birds have divided the breeding duties properly, Kasun Ekanayake and colleagues showed. During the day, the inconspicuous female breeds and only at night the male will take over. The one enemy that forages in the dark, the red fox, uses olfactory cues, and for this peril, it does not matter whether the father or the mother is sitting on the nest. Many clutches fall prey to the red fox, which isn’t a native species of Australia, but has been introduced and now poses a major threat to many bird and mammal species.

young red-capped plover is vulnerable to predatorsAs soon as the young red-capped plovers have hatched, they are mobile and they have to feed themselves. One of the parents is with them to keep them warm, to warn of danger and to lead them to places with food. The chicks fledge at approximately 35 days.

During the first few weeks after hatching, the chicks, which are camouflaged, are very vulnerable to predators. In that period, it is mainly the mother who accompanies them. Later, when the chicks become able to escape from danger, the father gradually takes over the care until they are independent. So, the care for the young birds seems to be equally divided between parents.

Wedding market

But there still is some inequality, as Daniel Lees and colleagues point out. For the division of care between parents, it matters whether they have daughters or sons.

The mother, who takes care of the chicks during the first weeks, will decrease her contribution over time at a lower rate when both young are males; in that case she continues to invest more than she would do if she had had two daughters or a son and a daughter. And the father, who gradually takes over her job, will provide more care if both young are female.

So, both parents care more for young of the opposite sex. No difference is to be seen between male and female chicks, and the researchers needed a blood sample to be able to determine the sex of the young. Apparently, however, the birds can distinguish between sons and daughters and treat them differently.

How to explain this? The researchers suggest that the parents may provide more care to young of the opposite sex because these young will not be rivals later on, on the wedding market. Fathers will then have to compete for attractive partners with their sons and mothers with their daughters. It is an possibility that still has to be investigated.

Willy van Strien

Photos:
Large: Red-capped plover, male. ©Daniel Lees
Small: Red-capped plover, chick. Benjamint444 (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Sources:
Lees, D., C.D.H. Sherman, K. Kostoglou, L.X.L. Tan, G.S. Maguire, P. Dann & M.A. Weston, 2018. Plover parents care more for young of the opposite sex. Behavioral Ecology, online April 5. Doi: 10.1093/beheco/ary052
Ekanayake, K.B., M.A. Weston, D.G. Nimmo, G.S. Maguire, J.A. Endler & C. Küpper, 2015. The bright incubate at night: sexual dichromatism and adaptive incubation division in an open-nesting shorebird. Proceedings of the Royal Society B 282: 20143026. Doi: 10.1098/rspb.2014.3026

Family ties

Caring treehopper mother recognizes her offspring

female treehopper, Alchisme grossa, guarding her eggs

Females of the treehopper Alchisme grossa exhibit complex maternal care. If a mother has been separated from her offspring, she can localize and recognize them, as Daniel Torrico-Bazoberry and colleagues show.

The treehopper Alchisme grossa occurs in Central and South America, where it lives on a number of host plants, feeding on plant sap. The females lay their eggs on the host plants; they cut a slit in the midrib at the underside of a leaf, deposit the eggs in it and cover the egg mass with a frothy secretion.

Alchisme grossa females exhibit extensive brood careThey then will exhibit extensive brood care for a few months, Daniel Torrico-Bazoberry and colleagues write. The caring behaviour is unique for such a small creature. A female positions herself over the eggs and shields them with an enlarged pronotum (dorsal plate of the thorax) which bears two horns at the front side. If parasites or predators, such as spiders or predatory bugs, try to reach the eggs of a guarding mother, she will behave like a hero. She moves her body, fans her wings and kicks with strong legs to scare off the enemies. A batch of eggs is certainly lost without its mother; if it does not fall prey to enemies, it will desiccate.

Sap feeders

The offspring rely on maternal care until they have completed development. The treehoppers undergo an incomplete metamorphosis. The nymphs that hatch from the eggs resemble adults, but are smaller. They undergo five instar stages before they are fully grown. Just like adult treehoppers, nymphs are sap feeders. Shortly before they hatch, the mother cuts a number of small holes in the midrib near the batch of eggs, so that the tiny nymphs can easily puncture the vein to tap the sap flow. And she stays with them. If the nymphs feel threatened, they drum on the leaf with their legs and the mother will come.

Now Torrico-Bazoberry shows that a female can localize and recognize her offspring after having been separated from them. This is useful, because often several females start a family on a single host plant, each on her own leaf. Torrico-Bazoberry put ten to fifteen nymphs from a single family on a host plant in the lab and a female on 20 centimetre distance on the same plant; in some cases she was the mother, in others she was not.

Trample

Separated from their mother, the nymphs often started to trample; one or a few began, the rest joined in producing a wave-like synchronized behaviour. Upon this rocking behaviour, the nymphs gathered. If the female that was put on the plant was their mother, they aggregated more closely; apparently they detected her presence. The female responded to the rocking behaviour if she was the mother: each mother approached the nymphs. Some non-mothers also did, but not all of them.

Nymphs of treehopper Alchisme grossa receive maternal care throughout developmentApparently, mother and nymphs discriminate kin from non-kin, probably on the basis of the composition of the chemical compounds of the outer skin layer, the researchers suggest. Chemical analyses revealed that this composition differs between individuals, differences between nymphs of a single family being much smaller than differences between nymphs of different families. Because the nymphs aggregate more closely in presence of their mother, it is easier for her to defend them and prevent them from desiccation.

Sometimes, the nymphs stay on their natal leaf until reaching maturity, but sometimes they disperse over the plant stem before that time. The mothers follow their young and together they form mixed aggregations with nymphs of other families and their mothers.

Willy van Strien

Photos: Treehopper Alchisme grossa. Andreas Kay (via Flickr. Creative Commons CC BY-NC-SA 2.0)
Large: female with eggs on midrib of leaf
Small, first: female
Small, second: older nymphs on plant stem

Sources:
Torrico-Bazoberry, D., L. Caceres-Sanchez, L. Flores-Prado, D. Aguilera-Olivares, F.E. Fontúrbel, H.M. Niemeyer & C.F. Pinto, 2018. Kin recognition in a subsocial treehopper (Hemiptera: Membracidae). Ecological Entomology, online Jan. 23. Doi: 10.1111/een.12506
Torrico-Bazoberry, D., C.F. Pinto, L. Flores-Prado, F.E. Fontúrbel & H.M. Niemeyer, 2016. Natural selection in the tropical treehopper Alchisme grossa (Hemiptera: Membracidae) on two sympatric host-plants. Arthropod-Plant Interactions 10: 229-235. Doi: 10.1007/s11829-016-9427-y
Torrico-Bazoberry, D., L. Caceres-Sanchez, D. Saavedra-Ulloa, L. Flores-Prado, H.M. Niemeyer & C.F. Pinto, 2014. Biology and ecology of Alchisme grossa in a cloud forest of the Bolivian Yungas. Journal of Insect Science 14: 196. Doi: 10.1093/jisesa/ieu031
Camacho, L., C. Keil & O. Dangles, 2014. Factors influencing egg parasitism in sub-social insects: insights from the treehopper Alchisme grossa (Hemiptera, Auchenorrhyncha, Membracidae). Ecological Entomology 39: 58–65. Doi: 10.1111/een.12060

Suicidal care

Spiderlings consume their aunts as well as their mothers

In Stegodyphus dumicola, unmated females provide extreme care to the offspring of other females

Females of the social spider Stegodyphus dumicola behave altruistically: not only mothers, but also virgin females show suicidal maternal care and are consumed by the spiderlings, Anja Junghanns and colleagues report.

The South-African spider Stegodyphus dumicola lives in large groups. Females construct a communal nest of silk and plant material with capture webs attached, collaborate in nest defence and share their prey. But when it comes to reproduction, tasks are divided: less than half of the females will mate and get offspring.

It was already known that the mothers take care of their young; they construct an egg sac, tend and guard it for a couple of weeks and when the young spiders have hatched, they regurgitate food for them. Eventually, they are even consumed by their offspring. Anja Junghanns and colleagues asked whether virgin females contribute to brood care, and to what extent. They composed groups of mated females and virgins, marked them with different colours and observed their behaviour.

Risky job

The virgins do perform maternal tasks, they noticed. Like the mothers, they guard the eggs, be it less intensive; instead, they engage more in prey capture than mothers, which can be a risky job. When the spiderlings have hatched, the unmated females, just like the genetic mothers, perform extreme care, regurgitating food – and being consumed eventually.

That willingness to perform ‘suicidal care’ for the young of other females can be explained by the high genetic relatedness among group members. A group mostly starts with a single mated female. Her offspring stay around and mate and reproduce within the nest, resulting in extreme inbreeding; sometimes a small group splits off. A group can grow to a size of more than a thousand members. By helping to care for other females’ offspring, virgin females enhance growth and survival of the spiderlings. Because of the high relatedness, the virgins that provide such help gain almost as much reproductive success as when they would have produced young themselves.

Moreover, they have no better option. The males of a generation mature and die early after hatching, while females mature asynchronously and many are slow. Mature males mate with females that have grown as fast as males, and for the many females that are late, no males are left and they remain unmated. So, the virgins have nothing to lose by helping.

Willy van Strien

Photo: Female with egg sac. ©Anja Junghanns

Source:
Junghanns, A., C. Holm, M. F. Schou, A.B. Sørensen, G. Uhl & T. Bilde, 2017. Extreme allomaternal care and unequal task participation by unmated females in a cooperatively breeding spider. Animal Behaviour 132: 101-107. Doi: 10.1016/j.anbehav.2017.08.006

In need of a ride

Tadpoles are in a great hurry to get away

A male splash-back poison frog transports each tadpole to a pool to grow up

Things go bad if sibling larvae of the splash-back poison frog Ranitomeya variabilis grow up together: only one of them will survive. So, as soon as an adult frog approaches, tadpoles try to climb on its back and to get a ride to a safe place, Lisa Schulte and Michael Mayer write.

Mating pairs of the splash-back poison frog Ranitomeya variabilis, that occurs in Peru, lay two to six eggs at the surface of small water bodies in plants, for instance Bromelia species. In such ‘phytotelmata’ the risk for the eggs to be found by a predator is small. Later, the male returns to retrieve each larva upon hatching and transports it on its back to an unoccupied phytotelm that he already selected. He then returns to fish the next larva out of the water, until all the young are singly housed in different phytotelmata.

Quickly

It is necessary for the larvae to get separated from each other, as the tadpoles are cannibalistic. If they stay together, only one of them will survive and grow up.

In some cases, however, the male doesn’t return to retrieve the hatching larvae. In such case, the abandoned tadpoles actively seek transport, as Lisa Schulte and Michael Mayer show. They collected clutches of eggs, took them to the lab and kept them in small plastic cups. After the tadpoles hatched, they were kept together and the researchers introduced an adult frog. That frog was either a conspecific male or a conspecific female, or a male of a different species.

In all cases, the tadpoles approached the adult frog, and many of them tried to climb onto its back quickly. Some succeeded. They actually jumped on the frog’s back, the researchers report; it looked like an attack.

High need

The tadpoles have a good reason to be so desperate. In a natural situation, a frog that shows up most likely is the male parent frog that revisits the phytotelm to save its young from cannibalism. The first tadpole to approach will be assisted to mount; the male will bend its back or push it up with its legs. After the male left with this lucky tadpole, there is no guarantee that he will return to get the other ones. If he can’t find an unoccupied phytotelm anymore, he will stay away. Hence the haste of the tadpoles.

But in the experiments, the visiting frog could also be a female, or a male of another species. In such cases, the tadpoles did not get any help. Yet they tried to get transport by mounting this frog on their own.

Obviously, the need to be saved is so high that the tadpoles don’t make any difference between their father and any other frog that happens to appear. And they had better not, because even a frog with no intention to bring tadpoles to a safe place may visit an unoccupied phytotelm, and rescue the hitchhiker.

However, when the researchers offered a plastic frog model, the tadpoles did not respond. They probably recognize a true frog by chemical cues.

Willy van Strien

Photo: John Clare (via Flickr. Creative Commons CC BY-NC-ND 2.0)

Source:
Schulte, L.M. & M. Mayer, 2017. Poison frog tadpoles seek parental transportation to escape their cannibalistic siblings. Journal of zoology, 5 mei online. Doi: 10.1111/jzo.12472

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