Variation in current versus future reproduction and tolerance to over-reproduction across a latitudinal cline in a burying beetle

Background/Question/Methods
We assess the cost of reproduction hypothesis using the burying beetle Nicrophorus orbicollis as a model organism looking at differences across latitudes to determine if reduction in the length of the reproductive season associated with increasing latitude have resulted in genetically based changes in life history strategies among populations.  Burying beetles reproduce on small vertebrate carcasses, which are prepared by the parents and serve as the sole source of food for both adults and offspring.  The parents assess carcass size and the number of offspring is accordingly culled to maximize the lifetime fitness of the parents. 

Results/Conclusions
As predicted by the cost-of-reproduction hypothesis (i.e. cost of allocation to current reproduction constrains future reproduction): individuals induced to miss-assess a carcass in favor of over-reproduction displayed a reduction in lifespan and lifetime fecundity when compared to females who did not.  Females provided with a larger carcass invested more in current reproduction than future reproduction.  Additionally, reproductive females showed a reduced lifespan when compared to non-reproductive females.  Consistent with the terminal-investment hypothesis, which suggests an increase in reproductive effort over somatic maintenance and survival in old individuals to maximize fitness prior to death, older females invested more heavily (in terms of number of offspring) to current reproduction than did younger females.  These general results were consistent for populations at differing latitudes.  Consistent with our prediction of life history variation between latitudes we observed smaller brood sizes in populations from more southern latitudes.  However, total number of lifetime reproductive bouts and life expectancy of reproductive females were greater at higher latitudes, in contrast to expected patterns.