LSM1303 Animal Behaviour

We all know that reptilian romances, like most Hollywood romances (Hello Jennifer Aniston and Brad Pitt!), do not last beyond  a single mating season. In fact, reptiles have the tendency to seek out various mating partners within a season (Madsen et al. 1992; Olsson 1995; Olsson and Madsen 1995). This points to a polygynous mating system in which the male mates with several females.

But unlike the serial-womanisers in Hollywood (Yes, I’m talking to you, Jude Law) who simply cannot keep their hands to themselves, polygyny within the reptilian community is linked to territoriality. Bull (2000) states the following:

In many lizard species males are also more active in the mating season because they are defending a territory. Dominant males can hold territories that contain the home ranges of several females…leading to a territorial polygynous mating system.

However, do not even for one second think that the ladies are then relegated to the passive role of being a member of the men’s harem. Female reptiles like the sand lizard (Lacerta agilis) are also known to mate with several males within a mating season (Olson and Madsen, 1995). The act of mating with several males is to ensure enhanced genetic variabilty among their offspring which will greatly improve reproductive successes.

So…is there “true love” in the reptilian kingdom?

I caught an episode of David Attenborough’s Life in Cold Blood series which documents the monogamous relationship between two Shingleback lizards (Tiliqua rugosa). The documentary prompted a quick search online for the Shingleback lizard and I came across Michael Bull’s article titled “Monogamy in Lizards” (2000), which also led me to Bull et al.’s article titled “Social monogamy and extra-pair fertilization in an Australian lizard, Tiliqua rugosa” (1998).

Before moving on to the discussion proper, here are some unknown facts of the Shingleback lizard. Below is an excerpt from Wikipedia:

Tiliqua rugosa is a short tailed and slow moving species of blue-tongued skink found in Australia. It has a heavily armored body and can be found in various colors, ranging from dark brown to cream. It is often seen sunning itself on roadsides or other paved areas.The skink is known by a variety of common names such as bobtail, shingleback or stump-tailed skink, bogeyes, and the Pinecone or Australian sleepy lizard. They have short, wide stumpy tails that resemble their head, and may confuse predators. The tail also contains fat reserves, which are drawn upon during hibernation in winter. The shingleback skink is an omnivore that eat snails and plants and spends much of its time browsing through vegetation for food.

Shingleback lizard

Knowing that prosmicuity is widespread within the reptilian community, it is even more shocking to know that Shingleback lizards are generally monogamous. I say “generally” because Bull et al. (1998) found that there exist certain cases of extra-pair copulation i.e. it was found that 79% of the females were with the same male partners while the remaining were found to be with different male partners. Still, I doubt the anomalous cases take anything away from how amazingly monogamous these creatures are. Bull (2000) describes the following:

Adult males and females of this species form monogamous pairs for an extended period before mating each spring, and they select the same partner in successive years.

If the mating pair gets separated, the male Shingleback lizard will attempt to track down the female by following her scent trail. When the male has finally located its mate, it was observed to nudge the female flank or back leg with its nose, and to tongue flick the female’s flank (Bull et al., 1993). In fact, Bull documents a story that took place in 1997 in which a male Shingleback lizard was found lying next to the carcass of a female Shingleback lizard who had died after being stuck in wired fence.

Bull proposed the following reasons for the monogamous bond between Shingleback lizards:

1. Having a single partner is advantageous because familiarity with the partner will improve one’s chances of feeding and detecting predators. (I figure that it’s somewhat like developing a certain chemistry with your significant other, one wouldn’t want to shop around for other mates if your current mate makes you happy. Seriously, why would you want to look for someone else if your current partner makes excellent spaghetti or helps you hold off the insane crowds during the Great Singapore Sale?)

2. The reason for “sticking” to a partner for years may be due to genetic compatibility. (This reminds me of the “Sweaty T-Shirts” video shown in class.)

3. Long term monogamy is also helpful in preventing the spread of parasites and diseases. An individual lizard would want to stay with a partner for many more years to come if it does not contract any diseases from that partner the first time round. (If you’ve been with a partner for years without contracting any sort of disease, chances are, you’d stay around him or her instead of actively searching for other partners who may have some forms of diseases . Then again, I should not give too much credit to humans, seeing how fickle we can be.)

So, is the monogamous partnership motivated by biological needs and concerns, or is there something more to it? You decide.

References:

Bull, C.M., Bedford, G.S. and Schulz, B.A., 1993. How do sleepy lizards find each other?. Herpetologica 49: 294–300.

Bull, C. Michael. Cooper, Steven J.B. Baghurst, Ben C. (1998). Social monogamy and extra-pair fertilization in an Australian lizard, Tiliqua rugosaBehav Ecol Sociobiol 44: 63-72

Bull, C. Michael. (2000). Monogamy in Lizards. Behavioural Processes 51 (1-3): 7-20

Madsen T, Shine R, Loman J, Hakansson T (1992). Why do female adders copulate so frequently? Nature 355:440-441

Olsson M (1995) Territoriality in Lake Eyre dragons Ctenophorus maculosus: are males “superterritorial”? Ethology 101:222-227

Olsson M, Madsen T (1995) Female choice on male quantitative traits in lizards – why is it so rare? Behav Ecol Sociobiol 36:179-184

Wikipedia.org

It is widely known that the only way to get a sex change is to have a surgical operation, but for chickens, they change their sex naturally, saving the cost for an operation! However, the known occurences are extremely rare, happening only in 1 out of 10,000 cases. “Every once in a while you hear a story about a hen that changed into a rooster. Such stories are often meet with skepticism, but sex reversals do, in fact, occur, although not very frequently,” says a 2000 report published by the University of Florida’s Institute of Food and Agricultural Sciences.

In an egg-laying barns where no roosters are present, a common behaviour arising from the hens are one of them will start crowing like a rooster. Generally, the hens only have one functional ovary, the left one, hence, once it is damaged, testorone will soar and regeneration occurs in the right gonad hypertrophies, which then regenerates as an ovotestis which consists tissues of either the testes or ovary, or both. This change is known as a spontaneous sex reversal and is extremely rare, usually happening only in barns which have a lack of roosters. The sex reversal will also occur when a rooster dies off and there is no rooster or a drastically small number of roosters left in the barn.

It is interesting to note that the hen will develop the behavioural and physical characteristics of the rooster as well. It will stop laying eggs, grow new plumage, a wattle and comb and starts the crowing behaviour. The sexually altered rooster will also try to mate with their old female mates. Although there are reports of the ovotestes producing semen and is able to reproduce, most however, are unable to reproduce.

Chicken run: George (1st in the photo) with some of the females he used to look like. The bird has become bossy since he swapped sexes and became a male Source: Daily Mail Reporter (http://www.dailymail.co.uk/news/worldnews/article-1080049/Pictured-The-sex-swap-chicken-called-Georgina-turned-cockerel-named-George.html)

Although majority of the sexually altered roosters are unable to generate semen to reproduce, the occurrence of this phenomenon is most probably to ensure a sexual balance in the brood or perhaps to maintain the need for a ‘boss’ figure in a brood of hens. However, it is intriguing to note that there are reports of these ovotestes having the ability to reproduce and another possible reason for the sexual change is to ensure reproduction is possible with non or few roosters in the brood to ensure continuation of its species.

Freaky- The sexually altered rooster

  Source: Bristol Evening Post

 (http://i7.photobucket.com/albums/y286/helena_the_chicken_lady/eveningPostChickenSexChange.jpg)

References:

1. Jacob, J and F. Ben Mather, 2000. Sex Reversal in Chickens. Department of Animal Sciences, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, FACTSHEET PS-53.
2. “The Sex-Swap Chicken Called Georgina that Turned into a Cockerel Named George,” by Daily Mail Reporter. Daily Mail Online, 23 October 2008.
3. “Letters: Sex-Change Chicken,” by M. A. Crooks. New Scientist, 16 May 1992.
4. “Strutting Super-Rooster is a Real Gender Bender,” by Geoff Bennett. Europe Intelligence Wire, 18 April 2006.

“This Can’t Be Love,” by Carl Zimmer. The New York Times, 05 Sep 2006.

The Daily Telegraph story on the Komodo dragon surprise of parthenogenesis in 2006 at Chester Zoo.

Source article: Watts, P. C., K. R. Buley, S. Sanderson, W. Boardman, C. Ciofi & R. Gibson, 2006. Parthenogenesis in Komodo dragons. Nature, 444: 1021-1022.

The New York Times story on parthenogensis in a hammerhead shark in Henry Doorly Zoo in Omaha, Nebraska in 2001. This was based on this 2007 paper: Chapman, D. D., M. S. Shivji, E. Louis, J. Sommer, H. Fletcher, P. A. Prodöhl, 2007. Virgin birth in a hammerhead shark. Biology Letters, 3 (4): 425-427.

See also the 2002 National Geographic story on the report of parthenogenesis in a white spotted bamboo shark at Bellle Isle Aquarium, Detroit.