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Posted by chrish on October 11, 2002 at 01:56:52:
In Reply to: Let's put our thinking caps on. posted by A.C. on October 10, 2002 at 00:42:16:
1. What is the biological advantage of a male indigo ripping apart his female mate to the point where she is dead or near death? How does this help the spp?
There doesn't have to be one. This is a common misconception regarding the actions of natural selection. It doesn't select for adaptive traits, it selects against maladaptive traits. So if an eastern indigo gains a mating advantage by grasping the female during mating (as do many other snakes), the fact that he "almost" injures the female doesn't impact her negatively enough to extinguish the behavior (in an evolutionary sense). If she survives and lays her eggs, the characteristic survives. Also, remember there are lots of other organisms with seemingly aversive mating behaviors. Have you ever seen film of nurse sharks mating! Ouch!
:2.Are there any valid reports of this occurrence in the wild?
Are there records of scarred females in the wild? I don't know for easterns and I've never looked closely at the TX indigo females I've found to check this.
3. Have we, captive breeders, bred these snakes like pitbulls with the meanest snakes siring our females to produce a meaner and meaner generation of males?
Eastern Indigos aren't currently, and haven't ever been bred in significant enough numbers in captivity to select for anything! And remember, almost every male indigo that gets born in captivity gets to mate, regardless of how mean he is or isn't. There isn't really any selection for this, other than the bottleneck imposed by the limited founder stock of the captive population. I seriously doubt that founder stock only consisted of aggressive breeding snakes.
We can certainly see sexual dimorphism. Basically in layman's terms, males are bigger in x species because x females only mate with the biggest strongest males.
This assumption may not be warranted in Drymarchon. Yes, in some sexually dimorphic species, male size influences mate choice by females. In other species, large males have the ability to defend more territory, so females aren't directly choosing the largest males, they are simply mating with the males whose territories overlap theirs. Males with large territories will mate with more females. In some species, that could be the larger males. For indigos, there isn't any data so it wouldn't be prudent to assume which pattern is responsible for the dimorphism, or if a totally different mechanism has resulted in the dimorphism seen.
