Research Accomplishment Reports 2007

Inbreeding and the Fitness Consequences of Colonizing Novel Environments in Herbivorous Insects

C.W. Fox
Department of Entomology

 

Project Description

In 2007 we completed a series of large breeding experiments to achieve our first two specific objectives, which are (1) To quantify the sensitivity of inbreeding depression to environmental conditions and (2) To test the effect of inbreeding associated with small population sizes on the purging of deleterious recessive alleles from insect populations.

Regarding objective 1, in a series of experiments we have found that the magnitude of inbreeding depression experienced by colonizing beetles is highly dependent on both temperature and the host being colonized. Most intriguingly, the influence of temperature varied with the rearing hosts. We are currently exploring the pest control implications of these results and will publish these results in 2008 and 2009.

Regarding objective 2, in two separate serially-inbreeding experiments, we have demonstrated that the degree to which deleterious recessive alleles can be "purged" (i.e., eliminated) from a population differs substantially among species. In particular, in the stored products pest, Callosobruchus maculatus, the "inbreeding load" (also called the "genetic load", the frequency of recessive alleles of deleterious effect) did not evolve in response to 5 generations of serial inbreeding. In contrast, in a native non-pest beetle that shares a quite similar life cycle (Stator limbatus) we could almost entirely eliminate the inbreeding load after only 4 generations of serial inbreeding. The S. limbatus results indicate that inbreeding depression in this species is due to a few genes that have large effects on larval survival, and which can thus evolve very quickly. However, the genetics underlying inbreeding depression must necessarily be different for C. maculatus, the pest species.

Impact

We are currently exploring hypotheses to explain the difference, and are exploring the degree to which the difference in genetics of inbreeding depression is a cause or consequence (if either) of the pest status of the insects. In 2007 we also executed our first experiment regarding objective 3, which is to test whether inbreeding associated with insect colonization of new environments exposes novel genetic variation to selection and thus influences adaptation to novel host species. This first experiment gave unclear results that will be further explored in new experiments over the next couple years.

Publications

Moya-Larano J, M El Tigani El-Sayyid & CW Fox. 2007. Smaller beetles are better scramble competitors at cooler temperatures. Biology Letters 3: 475-478.

Stillwell RC, GE Morse & CW Fox. 2007. Geographic variation in body size and sexual size dimorphism of a seed-feeding beetle. The American Naturalist 170: 358-369.

Stillwell RC & CW Fox. 2007. Environmental effects on sexual size dimorphism of a seed-feeding beetle. Oecologia 153: 273-280.

Stillwell RC, WG Wallin, LJ Hitchcock & CW Fox. 2007. Phenotypic plasticity in a complex world: Interactive effects of food and temperature on fitness components of a seed beetle. Oecologia 153: 309-321.

Carroll SP, AP Hendry, DN Reznick & CW Fox. 2007. Evolution on ecological time scales. Functional Ecology 21: 387-393.

Fox CW, KL Scheibly, BP Smith & WG Wallin. 2007. Inbreeding depression in two seed-feeding beetles, Callosobruchus maculatus and Stator limbatus. The Bulletin of Entomological Research 97: 49-54.

Carroll SP & CW Fox. 2007. Dissecting the evolutionary impacts of plant invasions: bugs and beetles as native guides. Global Change Biology 13: 1644-1657.

Fox CW, RC Stillwell & J Moya-Larano. 2007. Variation in selection and the evolution of sexual size dimorphism in two seed-feeding beetles. Pp 88-96 in DJ Fairbairn, W Blanckenhorn & T Szekely (editors) Sex, Size and Gender Roles: Evolutionary Studies of Sexual Size Dimorphism. Oxford University Press, Oxford.