Recent Projects
Mating signals are often complex suites of cues that may include any combination of visual, acoustical, tactical, electrical and/or chemical stimuli, varying in relative importance to mating decisions. Different components of the mating signal may provide information to receivers concerning species identity, gender, reproductive status and mate quality and mating signals may vary substantially across the geographic range of a species. How organisms use these signals to discriminate among potential mates has been of interest to students of animal behaviour for decades, but traditionally studies have focused on
Mating signal evolution
either interspecific mate recognition or intraspecific mate discrimination. In reality however, the process of mate choice is the same on both inter and intra-specific levels so interspecific mate recognition may be regarded as an extension of intraspecific mate choice.
Geographic variability in male and female visual courtship signals
Although interpopulation behavioral variability has been extensively documented for members of the threespine stickleback (Gasterosteus aculeatus) complex on the west coast of North America, little attention has been devoted to understanding the distribution and extent of behavioral variability in the other members of the stickleback family. Interestingly, the degree and temporal pattern of male coloration in at least one population suggests that the relative influences of natural and sexual selection have shifted in this group from courtship, to predominantly parental care and interpopulation differences in female nuptial colour are also apparent. The male agonistic and sexual behavioural repertoire performed during the courtship phase appears strikingly conservative, with most interpopulation differences manifested primarily as variability in performance parameters such as frequency of display and the loss of behavioural elements from the repertoire. Overall, our results imply that the brook stickleback is on a different evolutionary trajectory from that of its threespine cousin on the Pacific coast of North America.
In species with complex courtship, females often have the opportunity to assess multiple male cues during mate choice. Depending on the strength and form of the co-evolutionary relationships between male traits and female preferences, geographic variation in signal complexes can result in a variety of mate choice scenarios ranging from partial to complete positive assortative mating. Using mate choice trials, I investigated the relationship between intrapopulation female biases for complex visual signals and interpopulation mating dynamics in two populations of brook stickleback, Culaea inconstans, from distinct mtDNA genetic lineages. My results showed that courtship effort is the primary visual criterion of mate assessment in this species; females from both lineages exhibited directional preferences for increased behavioral vigor. In contrast, male nuptial color intensity and body size had little influence on female choice decisions. Interpopulation divergence in male traits was not strongly correlated with divergence in female preferences, producing asymmetric patterns of assortative mate choice across the lineage divide. Comparison of female preferences for male visual traits in C. inconstans with that of other members of the Gasterosteidae indicates that mate assessment differs substantially between stickleback species.
Sexual selection and female assessment based on complex traits
Body shape evolution
Using geometric morphometric methods, we evaluated the correlation between phenotypic variation and available historical and habitat information for two genetically differentiated, allopatric lineages of a widespread North American species, the brook stickleback (Culaea inconstans). Our results revealed strong patterns of structured phenotypic differentiation across the species range with extreme phenotypes occurring at the northwest and southeast range boundaries. Shape variation was broadly congruent with the distribution of two mtDNA lineages; a deep-bodied eastern form (Atlantic refugium) and a slim-bodied western form (Mississippian refugium), however, the two forms were not lineage-specific and phenotypic cladistic diversification is likely an artifact of underlying clinal variation associated with longitudinal and latitudinal gradients. In addition, we found little evidence of diagnosable lake and river forms across North America. Taken together, the results suggest that large-scale patterns of phenotypic diversity observed in C. inconstans are primarily the result of continually varying natural selection across the range and potential local gene flow, rather than historical separation or a generalized adaptive response to alternative habitats.
Nuptial colour evolution in sticklebacks
Male brook sticklebacks express intense black colouration during courtship. My previous research, however, revealed that females from at least two populations fail to exhibit a preference for more intense versions of this trait. Manipulating water spectral qualities, I found that females fail to show a preference for black males under clear, full-spectrum conditions. However, females strongly preferred nuptially coloured males in turbid, green-shifted spectral environments and tannin-stained, red-shifted spectral environments. This suggests that contrary to previous (but untested) assumptions, the function of the black nuptial signal is related to spectral contrast and is not an honest indicator of male quality.
