Hey. Like pafalafa, I'm a little unsure of what you are looking for
by your question and clarification. But I'd say that there is most
certainly a genetic basis to much of the cost of reproduction. In the
broadest sense, the genes that program for certain life histories or
certain phenotypic reproductive aspects bear directly on reproductive
costs and can supercede proximate resource-based factors. For
example, where iteroparous species can take advantage of an extended
favorable season (eg, abundant food) by engaging in multiple
reproductive bouts, semelparous populations cannot overcome their
genetically based spawn and die life history even if the proximal
environment favors a spawn and live strategy. Or, K-adapted organisms
with late onset of reproduction and/or large energetic investment in
few/large gametes will not be able to make a go of it if the
environmental stochasticity becomes such that they do not live long
enought reach sexual maturity or take in enough energy to pay for the
cost of gonad/gamete development. Similarly, phenotypes that confer a
presumable sexual selective advantage but also open animals up to
increased mortality risk should be seen as important tradeoffs. Male
coloration that can increase courtship success but make males more
susceptible to visual predators, perhaps. Or the textbook example of
the Irish elk, whose runaway selection of an extreme dimorphic trait
(massive male antlers) presumable led to an overall reduction in
fitness because survival took a hit - even if females prefered males
with the biggest racks.
Clearly, I'm leaning more toward crafting an argument in which genetic
factors are more important than environmental resources on
evolutionary scales. On proximal scales I think you can make the
opposite argument and it would be equally true. Resource limitation
(be it food, living space, nesting sites, mates...) is going to
largely determine the reproductive success in any given year.
Finally, it is the proximal environmental filter that, in time, gives
rise to the genotypes that dictate and constrain the specifics of
reproduction and so it comes full circle.
Aside: As far as what has been said earlier about "tickling apart"
the cost of reproduction (I like that terminology, btw), I would
disagree. Energy intake has to always be allocated between metabolic
basics (eg, respiration), growth, and reproduction. In a stressful or
resource-limited environment, reproduction (a 'luxury item') is the
first thing to go. As stress increases, growth is compromised.
Finally, if stress exceeds a lethal threshold the organism dies.
Picture it as three nested bell curves centered about an optimal mean
condition, and with increasing levels of stress extending in both
directions along the horizontal axis.
Apologies if my answers stayed somewhat generalized, but hopefully it
gives you some possible directions to go in. |
