Date Available

1-8-2024

Year of Publication

2023

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department/School/Program

Biology

First Advisor

Dr. David F. Westneat

Second Advisor

Dr. Charles W. Fox

Abstract

For populations in landscapes with increasingly heterogeneous and fragmented habitat patches (e.g., metapopulations), dispersal is an important behavior that leads to gene flow and connectivity among isolated patches. Because dispersal is a complex process, there are many traits involved. When suites of morphological, behavioral, physiological, and life-history traits covary with dispersal (e.g., a dispersal syndrome), the correlated traits can assist dispersing individuals through the complex process. Furthermore, once dispersal is completed, the correlated traits can influence the fitness of those dispersed individuals. Dispersal syndromes will likely interact with the local environment to produce ecological and evolutionary feedbacks on the metapopulation. Thus, for populations in heterogeneous landscapes, the nature of dispersal syndromes may be an important piece in establishing links between variation within a sub-population and the dynamics of multiple sub-populations within the broader metapopulation. My dissertation uses a seed beetle system to quantify a dispersal syndrome across multiple environmental contexts and between the sexes.

If dispersal syndromes are context-dependent, the direction and magnitude of correlations across a range of contexts may influence how much dispersal syndromes affect population dynamics. I artificially selected for long and short distance dispersal in female seed beetles (Callosobruchus maculatus, Coleoptera: Chrysomelidae, Bruchinae) then assessed correlated responses to selection in multiple life-history traits with dispersal behavior to quantify a dispersal syndrome in multiple environments (conspecifics absent, low, and high conspecific density). When looking for correlated responses to selection in life-history traits, only two traits were correlated with dispersal: beetles from dispersal-selected lines exhibited larger body sizes and shorter egg lengths compared to non-dispersal-selected lines. Only one trait (short-term fecundity) showed evidence of context-dependence. In an environment with high conspecific density, females from dispersal-selected lines laid fewer eggs than females from non-dispersal selected lines, but this difference was not detected in any other environment. My results indicate that, in seed beetles, dispersal syndromes and context-dependence of syndromes may be subtle.

To better understand the genetic basis of the traits that comprise dispersal syndromes and assess which traits are genetically correlated within and across the sexes, I measured dispersal behavior, body size, time to reach maturity, and reproductive output in male beetles from the populations artificially selected for long- and short-distance dispersal. For 3 traits, males evolved the same as females in response to selection, but interestingly there were 2 traits that males evolved differently from females: females from dispersal-selected lines made more location changes in a dispersal array than those from non-dispersal selected lines, but males from the lines did not differ; and females from the selection lines had similar fecundity, but males from dispersal-selected lines had a smaller spermatophore than males from non-dispersal-selected lines. Additionally, I found limited evidence that responses to selection are context dependent: males from the dispersal- and non-dispersal-selected lines had similar reproductive output regardless of conspecific density. In contrast, female reproductive output was higher for non-dispersal-selected lines than dispersal-selected lines when conspecifics are present, but this difference disappears when conspecifics are absent. The differences in male and female dispersal syndromes suggests that cross-sex genetic correlations are present but weak, and there is likely a combination of genotypic and environmental effects decoupling the traits in the dispersal syndrome.

By assessing context-dependent and sex-specific dispersal syndromes, I found that there is variation in dispersal syndromes of dispersal and non-dispersers that can depend on the environment. Future work should account for the variation among individuals in dispersal syndromes, beyond simply comparing disperser and resident syndromes. The variation among individuals (e.g., dispersal distance) combined with the complicated suite of traits that comprise a dispersal syndrome and interactions with the environment, makes assessing the impact of dispersal syndromes on metapopulation dynamics difficult. But integrating across biological levels (e.g., individual to subpopulation to metapopulation) is an important next step in metapopulation research.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2023.361

Funding Information

United States Department of Agriculture Pre-Doctoral Fellowship (Award Number: 2020-67034-31726) June 2020-June 2023

Department of Biology Merit Fellowship Aug-Dec 2017

Department of Biology Ribble Mini-Grant May 2017

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