Molecular mechanisms of self‐regulation in multiannual rodent populations: Experimental test of an updated hypothesis

In Focus Edwards, P. D., Frenette‐Ling, C., Palme, R., & Boonstra, R. (2021). Social density suppresses GnRH expression and reduces reproductivity in voles: A mechanism for population self‐regulation. Journal of Animal Ecology, 90, 784–795. Intrinsic population processes are important in the regulation of populations of small rodents, including those which display multiannual cycles. By measuring reproductive parameters, faecal androgen metabolites, and gene expression and DNA methylation in the CNS of juvenile voles, this paper demonstrates that suppression of reproduction occurs in female voles at high density compared to low density in enclosures, and that this maternal, epigenetic effect is also apparent in their offspring. This suggsests that direct density dependence influences reproduction and, hence, immediate rate of population growth, while gene expression mediated by DNA methylation blocking transcription, may have a delayed density‐dependent effect in juveniles. Both direct and delayed density dependence are necessary to generate multiannual population cycles. Edwards et al. (2021) break new ground in demonstrating the molecular and physiological basis of variation in population dynamics of small mammals ranging from multiannual cycles to stability that have fascinated researchers for nearly a century. This In Focus article highlights the work of Edwards et al. (2021). It addresses big questions in animal ecology which have been around for as long as the discipline. The authors have reinvigorated and updated an old hypothesis previsously discarded and tested it using good experimental designs and molecular methods. There is further work to do but there are clearly new directions in understanding population cycles to be explored.