Category: parental care (Page 3 of 3)

Tadpoles are in a great hurry to get away

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

A successful daddy longlegs is a bad dad

In Serracutisoma proximum, a species belonging to the harvestmen, the mother guards her eggs until the young have hatched. A male can do the job as well, but he does so only when he has nothing better to do, as Louise Alissa and colleagues report.

Many species of harvestmen (or daddy longlegs) exhibit a form of parental care: they protect their eggs. This is also true for Serracutisoma proximum, a species that inhabits the Atlantic forests of Brazil.

At the start of the breeding season, males try to establish a territory. They perform ritualised fights for the possession of an attractive area: two males face each other, extend their strongly elongated second pair of legs and try to hit each other. If one of them gives up and leaves, the other is the owner of the territory.

Harem

This male then has to wait for a female to arrive. When this happens, he copulates with her and she lays her eggs after fertilising them internally with his sperm. For a month, she will then stay and guard the clutch. That improves the survival, as conspecifics and other predators will eat many of the eggs when unattended.

On rare occasions, a female deserts or dies. The owner of the territory can take her place and tend the eggs, but there may be more important things for him to do, Louise Alissa and colleagues realised. A second female may visit the territory, and maybe still another. Around a successful male, a harem forms. The territorial male will copulate which each newcomer female as to increase his number of offspring, and he cannot tend a clutch and court newcomer females at the same time.

And that’s not all. There is also a need to guard a female after copulation until she has laid her eggs because of sneaker males, a second type of males (minors) that exist in addition to the territorial males (majors). Sneakers don’t fight for territories (and their second pair of legs is not strongly elongated), but they invade the territories of other males, especially when there are several females present, and try to furtively copulate with one of them to fertilise some of her eggs. The females lay almost all their eggs on the first day after mating with the territorial male, so continuous vigilance during this period is most important. Thereafter, sneaker males still have a chance to sire some young because a few late eggs appear during the next two weeks.

Deserted eggs

Because a successful male must pay attention to newcomer females, he will have less time to guard deserted eggs than a less successful male, the researchers hypothesized. To prove, they removed a egg-tending female from a number of territories that they had been observing for ten days. They then inspected these territories regularly to see whether the owners cared for the orphaned eggs.

As expected, males with only one or two females in their territory guarded the deserted eggs pretty well, while more successful males typically spent less time with the clutch. Males can do only one thing at a time.

Willy van Strien

Photos: ©Bruno A. Buzatto.
Large: two territorial males fighting
Small: caring male

Sources:
Alissa, L.M., D.G. Muniz & G. Machado, 2016. Devoted fathers or selfish lovers? Conflict between mating effort and parental care in a harem-defending arachnid. Journal of Evolutionary Biology, online November 7. Doi: 10.1111/jeb.12998
Munguía-Steyer, R., B.A. Buzatto & G. Machado, 2012. Male dimorphism of a neotropical arachnid: harem size, sneaker opportunities, and gonadal investment. Behavioral Ecology 23: 827-835. Doi:10.1093/beheco/ars037
Buzatto, B.A., G.S. Requena, R.S. Lourenço, R. Munguía-Steyer & G. Machado, 2011. Conditional male dimorphism and alternative reproductive tactics in a Neotropical arachnid (Opiliones). Evolutionary Ecology 25: 331-349. Doi: 10.1007/s10682-010-9431-0
Buzatto, B.A. & & G. Machado, 2008. Resource defense polygyny shifts to female defense polygyny over the course of the reproductive season of a Neotropical harvestman. Behavioral Ecology and Sociobiology 63: 85-94. Doi: 10.1007/s00265-008-0638-9

Mother transfers nutrients to the young in her dorsal pouch

Young of the live-bearing frog Gastrotheca excubitor are well taken care of. The mother carries them in a brood pouch on her back and provides them with nutrients, as Robin Warne and Alessandro Catenazzi show.

In many frog species, females lay their eggs in the water and then leave them alone. After hatching, the tadpoles take care of themselves. Parents of other species look after their young to some extent: the father or mother sees to it that the eggs, which are deposited above a water body, remain moist, or the parents carry the tadpoles to a suitable pool to grow up and bring them some food.

Brood pouch

A few species go even further: parents retain the young in or on their body until they have developed into froglets. One of them is Gastrotheca excubitor, a terrestrial marsupial frog of Central and South America. A mother carries the young in a brood pouch on her back and she transfers nutrients to them, Robin Warne and Alessandro Catenazzi report.

A male clasps a female that is about to lay eggs (amplexus) and fertilizes them when they come out. He then leads them into her dorsal brood pouch, a skin fold with an entrance at the rear. It accommodates more than ten eggs.

During pregnancy the brood pouch is sealed, so the eggs and, later, the hatchlings cannot take up oxygen from their environment. Respiratory gas is exchanged with the mother, as was already known, through the numerous blood vessels in the brood pouch membrane which folds over each egg. The eggs absorb oxygen through the egg membrane and hatchlings breathe through their large external and well vascularised gills that have fused to a ‘bell’. All nutrients the embryo needs are contained in the yolk, the idea was, as they are in other frog species.

Nutrients

But Warne and Catenazzi hypothesized that a mother provides her young also with nutrients, using the extensive network of blood vessels. Because she retains them for a long period – until they have fully developed into froglets – the amount of yolk may be insufficient, they reasoned. And experiments showed that this is true. The researchers fed pregnant frogs with insects that were chemically labeled (with rare isotopes of carbon and nitrogen, ¹⁵N and ¹³C), and found that the amounts of isotopes increased in the embryos. In addition, the developing froglets gained weight. So, nutrients must be transferred from mother to young.

More species of live-bearing frogs exist. In some species, the males swallow fertilised eggs and brood them in their vocal sac. There are also species in which the females ingest the eggs, which develop in their stomachs, and species in which froglets develop in the oviducts. Transfer of nutrients, however, is rare.

Willy van Strien

Photos © Alessandro Catenazzi
Large: mother with one of her emerged young
Small: larva

Sources:
Warne, R.W. & A. Catenazzi, 2016. Pouch brooding marsupial frogs transfer nutrients to developing embryos. Biology Letters 12: 20160673. Doi: 10.1098/rsbl.2016.0673
Wake, M.H., 2015. Fetal adaptations for viviparity in amphibians. Journal of Morphology 276: 941-960. Doi: 10.1002/jmor.20271