Showing posts with label reproduction. Show all posts
Showing posts with label reproduction. Show all posts

Tuesday, February 21, 2012

Fungal Ant Gardens as Incubators for Snake Eggs

Parental care in snakes is poorly documented. It has been known since the 18th century that female pythons will not only guard their eggs but warm them when the ambient temperature drops; female king cobras have been long known to build nests of decomposing vegetation for their eggs and stay nearby; and more recently maternal care in rattlesnakes has been observed. There are other examples scattered in the literature but perhaps most unexpected is the ancient scolecophidians show signs of parental care and since parental care is present in these snakes, the behavior should not be too surprising in the more modern snake lineages. Paleontologist Claude Hibbard discovered a nursery (or a communal egg laying site) of the New Mexico worm snake, Rena dissectus in the 1960’s.
A Liotyphlops albirostris egg on a colony of A. cf. goniodes.
Note that the workers have planted pieces of fungal garden on
the egg’s shell.

Recently Gaspar Bruner and colleagues report the dawn blind snake (family Anomalepididae) Liotyphlops albirostris depositing its eggs in the fungus gardens of the fungus-growing ant Apterostigma cf. goniodes.They found three snake embryos in the nest of the phylogenetically basal attine ant, which has relatively small nests. In an effort to determine if the ants could distinguish snake eggs from a snake-like egg made of a different material, the authors observed the behavioral responses of ants to natural and artificial snake eggs. They transferred the eggs from the nest to a sterile Petri dish and removed the fungal mycelium around the eggs using forceps. Then either a plasticine or natural egg (with the fungus removed), was placed on the top of the fungal garden. Using a stereomicroscope they observed the ants’ behavior toward the egg or the plasticine egg. They found worker ants repeatedly attended and groomed the snake eggs, but never observed the ants biting them. The ant workers took pieces of their fungus garden and planted them on the eggs, behavior very similar to what the workers do with ant eggs, larvae, and pupae in their fungus garden, as a means of controlling infections. When researchers removed the mycelial cover of an egg the ants completely recovered the eggs with fungal garden material and restored it to the original condition but did not attend or cover the artificial egg. Also, the ants spent substantially more time physically examining the snake egg than the artificial egg suggesting the ants were not simply responding to natural eggs as a foreign object. The entire article is available on line.


Tuesday, October 25, 2011

An Real Case of Sperm Storage in Eastern Diamondbacks

The New Scientist is carrying the following story. It is of interest because female snakes that have not been in contact with a male have produced offspring by parthenogenesis. Here is an apparent case of long term sperm storage. In most vertebrates sperm is thought to have a relatively short shelf life - unless of course the cells are placed in stasis, which some times happens in special sperm storage tubules.

FAMILY planning campaigners looking for a mascot should consider the eastern diamond-backed rattlesnake. A female of the species can store sperm in her body for at least five years before using it.

The rattlesnake (Crotalus adamanteus) in question was collected in Florida in 2005 and kept in a private collection for five years, with no contact with other snakes. In late 2010, she unexpectedly gave birth to 19 snakelets. To find out what had happened, Warren Booth of North Carolina State University in Raleigh took samples of DNA from the mother and her young.

Booth studies "virgin birth", in which a female produces young without any contribution from a male. But in this case the snakelets carried genes that their mother didn't, so she must have mated before she was captured and stored the sperm (Biological Journal of the Linnean Society, DOI: 10.1111/j.1095-8312.2011.01782.x).

Previous studies have hinted that reptiles can store sperm for several years, but this is the first case confirmed by genetics. Booth suspects other reptiles can store sperm even longer. "How long is anyone's guess," he says.It's becoming clear that snakes have unconventional ways of reproducing, including virgin birth and long-term sperm storage, says William Holt of the Institute of Zoology in London, though so far no one knows how they do it.

So much for the press release. In fact sperm storage in squamates has been relatively well studied. 

Oviducal sperm storage is known in females of all taxa of squamates except Amphisbaenia. However, in Rhynchocephalia and Crocodilia, sperm storage is poorly studied, and specialized sperm storage tubules (Ssts) are unknown. Sever and Hamlett (2002) used the molecular phylogenetic hypothesis [(Chelonia+Archosauria) (Squamata)] to trace evolution of sperm storage characters and found Ssts arose independently in Chelonia and Squamata. Turtles have albumen-secreting glands in the anterior half of the oviduct (the tuba or isthmus), and the most distal of these glands act as  Ssts; in addition, some turtles possess Ssts in the adjacent segment of the oviduct, the uterus. Squamates lack albumen-secreting glands, and the ancestral state is possession of Ssts in the posterior infundibulum (uterine tube). Secondarily, iguanids have evolved vaginal Ssts. They used ultrastructural observations on vaginal Ssts in lizards, with Anolis sagrei (Polychrotidae). Proximally, the neck of these simple tubular glands continues the alternation of ciliated and secretory cells lining the lumen of the vagina. However, the epithelial cells of the distal sperm storage area are neither secretory nor ciliated. The Ssts of Anolis are more similar to those of birds more than to infundibular receptacles in snakes and lizards.

Sever, D. M. and Hamlett, W. C. (2002), Female sperm storage in reptiles. Journal of Experimental Zoology, 292:187–199. doi: 10.1002/jez.1154

Wednesday, July 21, 2010

Florida Burmese Pythons are Regulating Egg Temperatures

The first report of a female Burmese Python using shivering thermogenesis in the wild has been described by Snow et al. (2010). The researchers placed data loggers in and around the brooding female python and found the female snake both warmed and cooled her eggs by generating body heat and cooling them through insulation.

Snow, R. W. et al. 2010. Thermoregulation by a brooding Burmese Python (Python molurus bivittaus) in Florida. Southeastern Naturalist 9(2):403-405.