Sexual selection in scaled reptiles
[2] In the species Japanese striped snake (Elaphe quadrivirgata), competition involves males maintaining body contact with their opponent and exerting pressure by pushing, topping, or entwining in order to subdue him.
The red-sided garter snake (Thamnophis sirtalis) population in Alberta, Canada hibernates for the majority of the year, emerging in early May to copulate and feed.
[1] Males who are able to align their body and cloaca, the joint outlet of the reproductive and digestive system, with that of the female for the longest period of time are often the most successful.
The increase in stress level causes cloacal gaping, allowing for the courting male to more easily insert his reproductive organ into the female.
Many researchers have assumed that multiple male courtships are successful without providing paternity evidence,[7] and mating systems may be more polyandrous, supported by studies of the green anaconda (Eunectes murinus).
When a female anaconda is ready to find a mate, she lies in an area of shallow water or mud until a male approached her.
These interactions sometimes lasted for periods of up to a month, showing that the males put a large amount of their energy into mating attempts.
[10] In the common collared lizard Crotaphytus collaris, males display their locomotive skills in order to attract a female by getting to territory and resources first.
Females prefer males that can afford to spend the most energy in displaying their traits because it is difficult to fake good genes.
[17] Experiments in which antioxidants were administered to these males led to the conclusion that breeding coloration reflects innate anti-oxidation capability that protects against oxidative damage to DNA.
[19] Snake tongues are bifurcated, or forked, to enhance their ability to pick up pheromones by means of tropotaxis,[19] and so are able to detect different stimuli intensities simultaneously using the two tips, flick them to pick up chemical cues from surrounding objects, which are delivered to the vomeronasal ducts upon reentry of the tongue into the oral cavity, activating the regions of the brain responsible for translation, allowing them to be processed and used for both mate and prey location.
A study done on prairie rattlesnakes, Crotalus viridis, indicates that males who maintain a constant search for females over fixed areas tend to be more successful in copulating.
[24] These chemical cues inform females of a male's quality,[25] with males trying to impress future mates by displaying elaborate colors, which can signal to a female that he is healthy, disease free, or has good genes,[26] as seen in the Dalmatian wall lizard Podarcis melisellensis, whose identity is based on their morph color: yellow, orange, the dominant colour as such lizards have a larger size and bite force so they can ward off competing males in order to mate with a female of choice and claim territory, and blue.
[27] In the species Uta stansburiana, throat coloration was also used as a way for males to elaborate their good health and body conditions to females.
[29] The male European green lizards develop a blue throat patch, which shows high reflectance in the ultraviolet (UV) range, which females prefer since throat brightness correlates with a larger body size, a larger head size and less ectoparasites,[30] though it is costly in energy.
[32] Size dimorphisms are common in snakes; females tend to be larger in populations where the production of large liters is feasible.
The male turtle headed sea snake, Emydocephalus annulatus, provides an interesting case study because of their unique scales.
Rugose skin provides a solution to this problem; its structure helps to increase the rate of oxygen diffusion, allowing for males to dive for longer periods.
[35] Snake sperm morphology and function is highly influenced by their ability to find, interact with, and fertilize eggs.
Snake species display extended copulations and higher gonad mass/body mass proportions in males than other reptilian taxonomic groups.
A common tactic in many species is to obstruct the reproductive pathway of the female in order to physically prevent additional copulations.
[41] A reason would be to ensure that her sons will have good genes that can display stronger more elaborate traits in order to maximize his reproductive success.
The semi-aquatic black swamp snake, Seminatrix pygaea, which lives in an environment where periods of drought are very common, has shown that environmental factors have a negative effect on female snakes whose large size was selected to increase fecundity as these droughts create a unique scenario to test whether survivability or reproductive pressures influence female body size more.
This correlates with the majority of Seminatrix pygaea giving birth at the start of the dry season, giving them some time to recover from the energy depletion they suffered from birthing clutches of offspring,[43] showing that selection favors smaller snakes in times of drought and larger snakes during years of high food abundance, and providing evidence that environmental factors affect sexual selection.
