From so simple a beginning

Evolution and Biodiversity

Month: March 2018

Deceit, abuse and benefits

28 March 2018 /

Complex relationships between arum, blowflies and lizard

Dead-horse arum flower is attractive to lizard

With its smell of rotting carrion, the dead-horse arum Helicodiceros muscivorus is irresistible to blowflies and a lizard. The blowflies will be abused, the lizard benefits. Ana Pérez-Cembranos and colleagues unraveled these complex relationships.

On islands in the Mediterranean Sea, a plant occurs with a very bad smell, the dead-horse arum, Helicodiceros muscivorus. Its odour contains chemical components that are also emitted by a decomposing dead animal. It irresistible to a female blowfly searching for carcasses to lay her eggs on to make sure that the carnivorous larvae will have food. The dead-horse arum takes advantage of that behaviour.

The plants release their odour on the first day of blooming. Blowflies that perceive the smell cannot ignore it. Upon approaching the source, they find a pink or red curved bract, the spathe, with the hairy end of the spadix (inflorescence), which produces the smell. When they land, the spadix turns out to be warm. To blowflies, the imitation is perfect: this is rotting carrion. Guided by the heat, they crawl into the tube that is formed by the base of the spathe around the lower part of the spadix, which bears female and male florets.

Trapped

Once inside, the blowflies don’t find what they need, which is decaying meat. But if they want to leave, they cannot. Spikes on the spadix keep the door closed. The blowflies are trapped.

Unintentionally, they provide a service to the arum during their imprisonment in the floral chamber. The female flowers at the bottom of the spadix are blooming this first day, and blowflies that had been misled by the arum before, now deliver the pollen that they picked up on that occasion. The plant has its female flowers pollinated.

The next day, the female flowers have faded and the male flowers are mature. The stench and the heat disappear, the spikes wilt and the blowflies escape, and while passing the male flowers, they are loaded with pollen. And here is the second benefit to the plant: the blowflies take the pollen with them to female flowers elsewhere – if at least they find another foul smelling arum on their way and are again misled into visiting it.

So, the blowflies are coerced to pollinate the dead-horse arum without receiving any reward such as nectar. On the contrary: they lose time that they should have spent on searching for genuine carcasses.

Basking

Now Ana Pérez-Cembranos and colleagues show that the Balearic lizard Podarcis lilfordi is also misled by the arum’s odour. The animal is omnivorous and sometimes forages on carcasses, which are also attractive as a heat source; lizards are cold-blooded and when the weather is cool, they may use a rotting carcass as a perching site for basking. In addition, they capture the blowflies that arrive at the cadaver in search for a site for oviposition.

The lizards respond to the smell of the dead-horse arum as they do to the smell of a carcass and will approach the source. If that turns out to be a dead-hors arum instead of a dead animal body, they will not find a meat meal, but they do find a basking place and blowflies, which they take from the spathe or grab from the tube. The lizards thus take away a number of pollinators, but, according to the researchers, enough are left to ensure pollination.

Fruits

So, the lizard isn’t an enemy of the arum. And after the flowering period, when fruits are ripe, a mutualism even develops between both. The lizards consume the fruits and disperse the seeds in their faeces; passage through the lizard’s intestine increases the probability of germination. On Aire Island, a the small island off the southeastern coast of Menorca, where the research was done, the dead-horse arum is a newcomer. It is estimated to have grown there for only about fifty years. In that period, it spread rapidly over the island and nowadays it locally occurs in great densities. That is because of the lizard, which has learned to eat the fruits and now is the main disperser of the seeds, the researchers think.

Willy van Strien

Photo: Balearic lizard on the spathe of the dead-horse arum © Ana Pérez-Cembranos

Sources:
Pérez-Cembranos, A., V. Pérez-Mellado & W.E. Cooper, 2018. Balearic lizards use chemical cues from a complex deceptive mimicry to capture attracted pollinators. Ethology  124: 260-268. Doi: 10.1111/eth.12728
Angioy, A-M.,  M. C. Stensmyr, I. Urru, M. Puliafito, I. Collu & B. S. Hansson, 2004. Function of the heater: the dead horse arum revisited. Proceedings of the Royal Society London B 271: S13-S15. Doi: 10.1098/rsbl.2003.0111
Stensmyr, M.C., I. Urru, I. Collu. M. Celander. B.S. Hansson & A-M. Angioy, 2002. Rotting smell of dead-horse arum florets. Nature 420: 625-626. Doi: 10.1038/420625a

Nutritious two-component glue

22 March 2018 /

Queen larva is firmly attached to her ceiling

Royal jelly, fed to a queen larva, holds her in place

A bee larva that is to become a queen receives large quantities of royal jelly. And that is not only because the stuff is nutritious, as Anja Buttstedt and colleagues show.

A female honeybee larva can become a worker or a queen, her fate depending on the food she receives. During the first days, all larvae are treated to the so-called royal jelly, a nutritious mixture that the nurse bees produce in their head glands; it is rich in proteins, sugars and fats. After the third day, larvae that will grow up to be worker bees are raised on a different diet. When they pupate, nurse bees close their cells with a layer of wax. But a larva that is destined to become a queen is fed on royal jelly exclusively; the nurse bees bring it to her in generous quantities. Thanks to that nutritious diet, she grows bigger than worker bees.

Queen cup

The royal jelly has still another function, Anja Buttstedt and colleagues discovered: it holds the queen larva in place.

And that is badly needed. The cells in the comb, in which worker larvae grow up, are too small for a developing queen larva. For her, the bee workers will build a special cell, a so-called queen cell or queen cup. It is not only wider, but also differently oriented: vertically, opening downwards. Therefore, her royal highness could easily fall out of her cell.

Buttstedt shows why that does not happen: the royal jelly, which the workers deposit on the ceiling, is so sticky that it keeps the larva hanging from the ceiling until it pupates and the cell is sealed with wax. The stickiness arises because two proteins, royalactin (the main protein in royal jelly) and apisimin, form long fibrous structures that make the jelly viscous.

Fiber network

The workers produce and store the proteins in their hypopharyngeal glands. The gland mixture is liquid, enabling the bees to excrete it. But when they deposit it in a brood cell, they combine it with fatty acids which they produced in the mandibular glands, and in those acidic conditions, the proteins royalactin and apisimin form a fiber network.

So, royal jelly is a two-component adhesive, as the authors conclude, serving as excellent food as well. It is just what a queen larva needs to grow up safely.

Willy van Strien

Photo: Honeybee, comb and two queen cells. Piscisgate (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Source:
Buttstedt, A., C.I. Muresxan,H. Lilie, G. Hause, C.H. Ihling, S-H. Schulze, M. Pietzsch & R.F.A. Moritz, 2018. How honeybees defy gravity with royal jelly to raise queens. Current Biology, online March 15. Doi: 10.1016/j.cub.2018.02.022

Helpers in the nest

16 March 2018 /

Thanks to helpers, cichlid mothers acquire more food

In Neolamprologus obscurus, young fis stay with their mother to help

When young of the cichlid species Neolamprologus obscurus have grown up, they are allowed to remain in the territory of their mother for a while because of their help. Hirokazu Tanaka and colleagues wanted to know why that help is important.

Neolamprologus obscurus, a cichlid fish that occurs in Lake Tanganyika in Africa, lives in groups in which each breeding female owns a territory along a steep bank, where she has dug out several cavities under stones. In those safe shelters, she spends almost all her time and she uses them for breeding. She guards her eggs and fry, and chases conspecifics out of her territory.

But her grown up young are allowed to stay. They help her defend the territory and maintain the shelters by removing sand that continuously enters from the edges.

Tiny prey

The removal of sand from the shelters is most beneficial to her, Hirokazu Tanaka and colleagues discovered. The shelters not only serve as a safe residence and as a breeding ground, but they are also a means to acquire food. The fish feed on small benthic invertebrates, especially shrimp. These tiny animals move up to the water surface at night to forage, but in the full light of the day they are not safe there and before dawn, they sink back to the bottom to hide in cracks and cavities – such as cavities in which Neolamprologus obscurus lives. The food comes to the fish by itself.

Tanaka shows that the larger a cavity is, the more benthic invertebrates immigrate at dawn. Because of this increased food abundance, it is desirable for a breeding female to have helpers that maintain the shelters and even enlarge them.

Content

Of course, helpers take some of the food that they acquire, so part of the gain is lost for the breeding female. But she still profits, because the more helpers are present to remove sand from the edges of the cavity, the longer those edges can be. And the area and content increase even more: with a double number of diggers, maintaining a cavity with a circumference that is twice as large, the area and the volume become four times larger, and as a consequence, more food is available per fish when more helpers are around.

But there is a limit to the number of helpers a female will tolerate; it will be no more than ten. So, when young fish have become larger, they will disappear from her territory to start for themselves.

Willy van Strien

Photo: Neolamprologus obscurus, helper. ©Hirokazu Tanaka

Sources:
Tanaka, H., J.G. Frommen & M. Kohda, 2018. Helpers increase food abundance in the territory of a cooperatively breeding fish. Behavioral Ecology and Sociobiology 72: 51. Doi: 10.1007/s00265-018-2450-5
Tanaka, H., J.G. Frommen, L. Engqvist & M. Kohda, 2017. Task-dependent workload adjustment of female breeders in a cooperatively breeding fish. Behavioral Ecology 29: 221–229. Doi: 10.1093/beheco/arx149
Tanaka, H., D. Heg, H. Takeshima, T. Takeyama, S. Awata, M. Nishida & M. Kohda, 2015. Group composition, relatedness, and dispersal in the cooperatively breeding cichlid Neolamprologus obscurus. Behavioral Ecology and Sociobiology 69: 169–181. Doi: 10.1007/s00265-014-1830-8

Males in transition

8 March 2018 /

Squid male changes its mating tactic when growing larger

Males in the squid Doryteuthis pleii adopt alternative mating tactics, depending on their age

When becoming sexually active, male squids are little successful at first. Only later they perform better, increasing their chances to sire offspring. This development includes major changes, Lígia Apostólico and José Marian discovered.

In squid like Doryteuthis pleii, a species living off the coast of Brazil, small males are able to mate, but they have to do it at an inappropriate time and in a little successful way, as sneakers. Large males act much more effectively as real partners or consorts, as Lígia Apostólico and José Marian report.

Shooting mechanism

When squid mate, s male delivers sperm packages to a female. With a special arm, a male takes the packages, spermatophores, from the spermatophoric sac, where they are produced, and places them on the body of a female with a rapid movement. Then he is done, the sperm packages themselves will do the rest of the work. With a shooting mechanism (ejaculatory apparatus), a package turns inside out, and when evaginated, it attaches onto the female’s body and the sperm cells swim out.

A large male delivers its sperm packages neatly. He approaches a female that is about to release her eggs, places himself next to her with his head pointing in the same direction as hers, moves his special arm behind her head under the mantle that surrounds her body and places his spermatophores near the opening of the oviduct from which the eggs will be released in capsules. The sperm cells have immediate access to the eggs. The male guards the female and tries to keep rivals at bay with flickering colour patterns, because if another male also mates with her, his sperm will have to compete with that other male’s sperm.

Aggregate

A small man does not stand a chance against a large one, so he can only mate at a less exciting time, when no eggs are to be released soon. He doesn’t put his arm under the female’s mantle, but he assumes a head-to-head position and places his sperm packages under her beak, that is between the arms. When she releases the eggs, she holds the capsules for a while near the beak before depositing them on the substrate, and then a sneaker’s sperm cells have a chance – as far as the eggs are not fertilized already by a consort’s sperm.

The sperm cells of sneakers are adapted to the unfortunate site where they are placed and the wide time interval between mating and fertilization chances, and their spermatophores differ from those of consorts. Sneakers have smaller and thinner spermatophores; after evagination, they are short and club-like shaped. The sperm cells come out slowly and aggregate at the exit, having nothing to do there for the time being. The spermatophores of consorts, in contrast, are larger and after evagination, they are long and hook-like shaped. The sperm is quickly discharged in a powerful flow and sperm cells immediately diffuse, so the eggs that are released will pass through a cloud of them.

Now in Doryteuthis pleii, Apostólico and Marian found some males, intermediate in size between sneaker and consort (about 17 centimetres mantle length), that produce sneaker-like spermatophores as well as consort-like spermatophores, and often also an intermediate form. The sneaker-like packages are oldest and stay in the anterior part of the spermatophoric sac, the consort packages are youngest and reside in the posterior part, and the intermediate packages are to be found in between.

Fast switch

This indicates that a male starts as a sneaker and, if he exceeds a certain size limit, he will go on as a consort, implementing all changes that are required by the transition. Age estimates show that sneakers are indeed younger than consorts; the estimates are based on the size of small particles in the organs that enable the animals to control their position and balance; every day these particles, statoliths, increase a little in size. The switch from sneaker to consort must take place very fast, as only few males are found that are in transition.

So, during their lives, which lasts less than a year, the males go through a major development. They are small when at summer the mating season starts, but still they mature sexually, so that they can begin to reproduce – although for the time being only as little successful sneakers.

But perhaps not all males follow that path, Apostólico and Marian think. Males that were born early, in late summer or autumn, have much time before the mating season starts. They can grow to a large size before they become sexually active, and then they can be consorts from the start.

Willy van Strien

Photo: Alvaro E. Migotto (Cifonauta. Creative Commons CC BY-NC SA 3.0)

Sources:
Apostólico, L.H. & J.E.A.R. Marian, 2018. From sneaky to bully: reappraisal of male squid dimorphism indicates ontogenetic mating tactics and striking ejaculate transition. Biological Journal of the Linnean Society 123: 603-614. Doi: 10.1093/biolinnean/bly006
Apostólico, L.H. & J.E.A.R. Marian, 2018. Dimorphic male squid show differential gonadal and ejaculate expenditure. Hydrobiologia 808: 5-22. Doi: 10.1007/s1075
Apostólico, L.H. &  J.E.A.R. Marian, 2017. Dimorphic ejaculates and sperm release strategies associated with alternative mating behaviors in the squid. Journal of Morphology. 278: 1490-1505. Doi: 10.1002/jmor.20726

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