Differences in lifetime reproductive output on varying resource sizes in a burying beetle

Background/Question/Methods

Burying beetles are excellent model organisms for studying life history traits because of their unique biology (biparental care on a discrete resource) and their ease of manipulation in both the laboratory and field settings.  Many species of burying beetles coexist and face potential competitive interactions as they attempt to locate and reproduce on small mammal or bird carcasses.  Because of tradeoffs between offspring size and number, as well as current vs. future reproduction, certain carcass sizes are expected to optimize lifetime reproductive output for each species.  Competitive interactions would likely drive niche partitioning among sympatric species, a potential result being optimal lifetime reproductive output on different sized carcasses.  Here, we investigate in a laboratory setting lifetime reproductive output in one species of burying beetle, Nicrophorus guttula, from a population in central Utah.  From wild individuals, we established a reproductive lab population and raised females on one of six different carcass sizes over their lifetime.  For each female, we measured number of reproductive bouts, number and size of offspring for each reproductive bout, and change in female mass after each breeding attempt.

Results/Conclusions

Lifetime reproductive output differed significantly for different sized carcasses.  Lifetime reproductive output optimized on small to mid-sized carcasses and was reduced on larger sized carcasses.  Beetles reproducing on larger sized carcasses tended to have fewer reproductive bouts than those reproducing on smaller sized carcasses.  Beetles also experience more frequent brood failures later in life than during early reproductive attempts, suggesting senescence.  Future work will investigate variation in optimal carcass size among species.  Differential use of carcasses based on size may be a mechanism for reducing competition among species.