Showing posts with label adaptations. Show all posts
Showing posts with label adaptations. Show all posts

Tuesday, August 30, 2011

The Impact of Climate Change on Four Species of Snakes

Bitis nasicornis. JCM

The prediction that climate change will have dramatic impacts on organisms has been discussed for a while. Three new studies support the idea that climate change will greatly influence snakes and how they will adjust to changes in habitat, competitor abundance and changes in the available food supply. These changes are occurring now and will continue into the future. 

Pierluigi Bombi and colleagues have two papers (Bombi et al. 2011a,b). In the first they report (Bombia 2011a) that the most endangered snake in Italy, the Sardinian Whipsnake, Hemorrhois (= Coluber) hippocrepis, is threatened by human alteration of its habitat and suggest that this is exacerbated by climate change. In Italy, the species in known only from the southern end of Sardinia. While nothing is known about the potential effects climate change could exert on this species, ecological modeling of its habitat suggested climate changes will greatly alter the snake's remaining habitat. Changing climate conditions will cause a dramatic reduction of suitable habitat by 2020, with a further collapse by 2050 (down to 11 km2). They found only one existing protected area will likely retain suitable habitats for this species.

In a second article, Bombi et al. (2011b) used data collected over the past 15 years on the ecology and population abundance of the Gaboon viper (Bitis gabonica) and the Nose-horned Viper (Bitis nasicornis) in southern Nigeria. The field work found several high-abundance and low-abundance populations of these two species. The authors analyzed the potential effects of climate change by modeling the current dataset on viper abundance (both high and low) using generalized additive models. Using climatic surfaces of current conditions as spatially explicit predictors, they projected viper abundance into a future climatic scenario. The future climatic conditions seemed appropriate for the success of the climatic niche used by the high-abundance Gaboon viper in their study area. While the future climatic niche for the high-abundance nose-horned viper populations was predicted narrow. In future scenarios, the two species were predicted to have a larger overlap in their climatic niche, and this is likely to increase interspecific competition.

Beata Ujvari at the University of Wollongon and colleagues (2011) note that climate change can result in the movement of resources critical for the viability of a population, and a species' resilience to such changes will depend upon its ability to shift its activities away from no-longer-suitable sites to exploit new opportunities. Common sense would suggest that predators should be able to track spatial shifts in prey availability, but data on water pythons (Liasis fuscus) in tropical Australia suggest a less encouraging scenario. Water Pythons undergo seasonal migrations that may cause them to move up to 10 km, following flooding-induced migrations by their prey, the Native Dusky Rats (Rattus colletti). However, when an extreme flooding event virtually eliminated the rats for three years, the local pythons did not disperse despite the presence of abundant rats only 8 km away; instead, many pythons starved to death. This inflexibility suggests species that track seasonally migrating prey may do so by responding to habitat attributes that have consistently predicted prey availability over evolutionary time, rather than reacting to proximate cues that signal the presence of prey per se. Therefore, a species' vulnerability to climate change will be increased by an inability to shift its activities away from historical sites toward newly favorable areas.

Literature

Bombi, P.and Capula, M., Amen, M and Luiselli, L.. 2011a.Climate change threatens the survival of highly endangered Sardinian populations of the snake Hemorrhois hippocrepis. Animal Biology 61:239-248.
Bombi, P., Akani, G. C., Ebere, N., Luiselli, L. 2011b. Potential effects of climate change on high- and low-abundance populations of the Gaboon viper (Bitis gabonica) and the nose-horned viper (B. nasicornis) in southern Nigeria. The Herpetological Journal 21:59-64.

Ujvari, B., Shine, R., Madsen, T.. 2011. How well do predators adjust to climate-mediated shifts in prey distribution? A study on Australian water pythons. Ecology 92:777–783. [doi:10.1890/10-1471.1]

Sunday, April 3, 2011

Eggs & Tadpoles of the Indian Brown Frog

The Indian Brown Frog, Indirana semipalmata. 
Photo Credit: 
L. Shyamal
A metamorphosing Indirana semipalmata.
 Photo Credit: L. Shyamal
Indirana is a genus of about 11 species endemic to the Western Ghats of southern India that usually breed in the splash zone of streams, the tadpoles are semi-terrestrial, using water that condenses on leaf litter, rocks, soil and other surfaces. They have been placed in the families Ranidae and Ranixalidae. Indirana semipalmata inhabits Tamil Nadu and Kerala in southern India and by all accounts it is relatively common and widespread at elevations between 200 and 1,100 meters above sea level. The adults are terrestrial in the leaf-litter of tropical forests and swamps and it has been recorded in coffee plantations and secondary forest. Ben Tapley of Wildlife.com is reporting that in July of 2010 an amphibian ecology study at the Agumbe Rainforest Research Station (ARRS) in Karnataka, India (http://www.agumberainforest.com/) found several egg clutches and tadpoles of this frog that were laid on the bark of a tree. Tadpoles from another clutch were observed feeding on the bark of the same tree. Three clutches of  Indirana semipalmata eggs were at least 3 m away from any standing water, and they suggest this is the first recorded case of tadpoles feeding on a bark substrate and subsequently metamorphosing on the bark of a tree. Tapley suggests this may be a localised phenomenon as Agumbe has the second highest annual rainfall in India and therefore these semi terrestrial tadpoles do not desiccate. Living in Agumbe during the monsoon was literally like living in a cloud. However, since these frogs have evolved in this environment, it would seem likely that this is their life style, and it raises the question of exactly what are the tads eating? Are they actually eating the bark or, more likely in my opinion algae, fungi, or other protists growing on the tree's surface? Also, because of the habitat difference - laying eggs on trees, instead of stream side rocks reported for other populations, it suggests this population could be a different species.

Wednesday, December 8, 2010

Snakes & Snails

Relatively few snakes feed on mollusks, but there are snakes in many lineages that have specialized to feed on gastropods. In North America the natricids in the genus Storeria feed on slugs and earthworms, in the Neotropics some of the dipsidids (Sibon, Dipsas, Tropidodipsas, and Sibynomorphus) tend to specialize in feeding on snails and slugs. In Africa members of the genus Duberria (family Pseudoxyrhophiidae) feed on slugs, However, the Asian family Pareatidae are very specialized for feeding on gastropods, and Pareas iwasakii has been well studied by Masaki Hoso and colleagues (see references below).

Above: Pareas iwasakii grasping a snail. 
Below: The skull and lower jaws of Pareas
iwasakii,  note the different number of teeth 
on each side of the jaw. From Hoso et al. (2010).
Snails with shells that coil counterclockwise have difficulty mating with snails of the same species whose shells coil clockwise because their bodies do not align properly. The snails have traded easy of mating for safety from snakes. The coil direction made mating difficult, and why a mutation causing this reversal would be favored was puzzling. Most snail shells curl clockwise. Studies of Iwasaki's Snail-eater (Pareas iwasakii) demonstrated the snake approaches the snail from behind, grasping the shell with its upper jaw and the soft body with its lower jaw. The snake then works the right and left halves of its lower jaw back and forth to extract the snail's body from the shell.

Since most snail shells turn clockwise, the snakes evolved a specialized lower jaw with more teeth on the right side than on the left. This makes it difficult for the snake to feed on snails coiled counterclockwise. When snakes try and eat snails coiled counterclockwise they frequently fail, and often drop the prey. In one study 87.5 percent of the counterclockwise snails survived the snake, suggesting the spiraling made the difference.

In a follow-up to the previous work Hoso et al. (2010) examined the snails and how genes can spread in a population. The land snails have a single gene for left–right reversal and the authors suggest that this could result in instant speciation, because dextral (shells coiled to the right) and sinistral (shells coiled to the left) snails have difficulty in mating. Hoso and colleagues show that specialized snake predation of the dextral majority drives prey speciation by reversal. Their experiments demonstrate that sinistral Satsuma snails (Stylommatophora: Camaenidae) survive predation by Pareas iwasakii. They found stylommatophoran snail speciation by reversal has been accelerated in the range of pareatid snakes, especially in snails that gain stronger anti-snake defense and reproductive isolation from dextrals by sinistrality. Molecular phylogeny of Satsuma snails further provides intriguing evidence of repetitive speciation under snake predation.

Literature
Hoso, M. 2007. Oviposition and hatchling diet of a snail-eating snake Pareas iwasakii (Colubridae: Pareatinae). Current Herpetology 26:41–43.

Hoso, M. and M. Hori. Divergent shell shape as an antipredator adaptation in tropical land snails. American Naturalist 172:726–732.

Hoso, M. and M. Hori. 2006. Identification of molluscan prey from feces of Iwasaki's slug snake, Pareas iwasakii. Herpetological Review 37:174–176.

Hoso, M., T. Asami, and M. Hori. 2007. Right-handed snakes: convergent evolution of asymmetry for functional specialization. Biology Letters, 3:169-172 DOI: 10.1098/rsbl.2006.0600

Hoso, M.,Y. Kameda, S.-P. Wu, T. Asami, M. Kato, and M. Hori. 2010. A speciation gene for left–right reversal in snails results in anti-predator adaptation. Nature, http://www.nature.com/ncomms/journal/v1/n9/full/ncomms1133.html