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Genetics of speciation in sympatric char; population genomics; conservation
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Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - Nov 2019)
No abstract available.
No abstract available.
In sperm-dependent asexual reproduction, sperm is not required for its genetic contribution, but it is required for stimulating zygote development. In my dissertation, I address several questions related to the coexistence of sperm-dependent asexuals and the sexually-reproducing species on which they depend. I have focused my research on a sperm-dependent asexual fish, Phoxinus eos-neogaeus, that originated via hybridization between P. eos and P. neogaeus.Using a mathematical model of mate choice among sexuals and sperm-dependent asexuals, I showed that stable coexistence can occur when there is variation among males in the strength of preference for mating with sexual females and when males with stronger preference pay a higher cost of preference. My model also predicts that coexistence is facilitated when the asexuals suffer a fitness disadvantage relative to the sexuals. Subsequent empirical work, in which I compared the repeat swimming performance, fecundity, and growth rate of asexual and sexual Phoxinus, provided results that are consistent with this prediction: the asexuals are, at best, as fit as the sexuals.I sampled Phoxinus populations from across the species’ North American distribution and the pattern of mitochondrial DNA variation across these populations suggests that all P. eos-neogaeus have originated from hybridization events that took place in a Mississippi River glacial refugium. Also, cytoplasmic hybrids (which are P. eos with P. neogaeus mitochondrial DNA) appear to have replaced ‘pure’ P. eos in all northern populations, which may reduce the disparity in fitness between P. eos-neogaeus and their sperm donors if P. neogaeus mitochondria are adapted to northern environments. The pattern of nuclear DNA variation across P. eos-neogaeus populations suggests that those using P. eos sperm are genetically distinct from those using P. neogaeus sperm. These genetically distinct populations match their host species in size, suggesting that sperm-dependent asexuals may be adapted to be proficient at soliciting sperm from particular sexual species.Persistence of sperm-dependent asexuals depends on stable coexistence with sexual species. My work highlights the importance of the relative fitness of asexual and sexual species, and of male mate choice in maintaining this stable coexistence.
Master's Student Supervision (2010 - 2018)
Resource polymorphism and natural hybridization are evolutionary phenomena that play an important role in the development of reproductive isolation during speciation. The Arctic char (Salmonidae: Salvelinus alpinus) exhibits substantial phenotypic and genetic diversity across its Holarctic range, making it an ideal species to examine the role of intraspecific trophic polymorphism in driving reproductive isolation and the interactions between hybridizing species in sympatry. In one southwestern post-glacial lake previously analyzed for resource polymorphism (Lower Tazimina Lake), I found evidence for two genetic groups of char and for significant differences in the distribution of microsatellite variability among at least two of the three previously described body-size morphotypes (‘large’, ‘medium’, and ‘small’–bodied char; maximum FST = 0.09). I also found significant associations between genetic type and gill raker counts among body-size morphs (r = -0.73, P
No abstract available.
The Cultus pygmy sculpin (Cottus aleuticus) is endemic to Cultus Lake, southwestern BC, and is listed as threatened under the federal Species at Risk Act (SARA). The Cultus pygmy sculpin was first discovered by Ricker in the 1930’s (Ricker 1960) and was described as a dwarf coastrange sculpin (C. aleuticus). It matures at a smaller size than the “normal” C. aleuticus; has a lacustrine rather than a fluvial life history; and appears to undertake diurnal feeding migrations into the water column to feed on the abundance of Daphnia. The Cultus pygmy sculpin also has different morphological features, including larger cephalic pores, shorter pelvic fins, and a greater number of pectoral fin rays, which may be advantageous for an open-water, planktivorous lifestyle. Little else, however, is known of the biology of this fish. I used mtDNA and microsatellite analyses to determine whether there is any genetic distinction between the pygmy sculpin and the coastrange sculpin. Potential behavioural differences between the two forms were also examined by comparing vertical depth selection in the laboratory, with and without Cottus asper, a benthic predator found in Cultus Lake. Results from combined microsatellite and mtDNA analyses indicate that there is no clear phylogeographic separation between pygmy and coastrange sculpin, but that there is genetic differentiation at the population level. Pelagic sculpin from Lake Washington were compared with the Cultus pygmy sculpin and showed divergence from it, which suggests that the pelagic life history has evolved independently in each lake. The Cultus pygmy sculpin was found significantly higher in experimental depth selection tanks than the stream forms of C. aleuticus, but only when C. asper was also present in the tanks. Taken together, molecular and behavioural results indicate that the Cultus pygmy sculpin is discrete from the coastrange sculpin, and validate its recognition as a conservation unit distinct from “typical” C.aleuticus. The presence of abundant planktonic prey within the water column of Cultus Lake, combined with the presence of predators on the lake’s bottom, may be important features of the lake that have promoted the evolution of pelagic behaviour by the Cultus pygmy sculpin.
Southwestern British Columbia is unique in that it is apparently the only place on Earth with sympatric species pairs of threespine stickleback (Gasterosteus aculeatus). As such, these species pairs are listed as endangered and are protected under Canada’s Species at Risk Act. Historically these species pairs inhabited seven known lakes but their distribution is currently limited to five lakes in three watersheds. Within these lakes stickleback are found in two forms: benthic and limnetic. These species pairs are thought to have originated through a double-invasion process followed by character displacement. While this hypothesis is supported by morphology and genetics it does not take into account the environmental factors needed to support threespine stickleback in two separate microhabitats, which may be essential for their continued persistence. It is conceivable that the divergence and persistence of the threespine stickleback species pairs may be due in part to unique environmental characteristics of the lakes they inhabit, including physical lake characteristics, water chemistry, or biological productivity. Alternatively, divergence and persistence could be due to specific attributes of fish community structure or random colonization events unrelated to lake attributes. To establish this, I measured a number of abiotic (water chemistry, physical lake parameters) and biotic (food resources, macrophyte abundance) variables from both species pair and non-species pair threespine stickleback lakes in order to identify any factors that may discriminate species pair lakes from non-species pair lakes, thereby leading to a clearer understanding of their critical habitat. While I did not find any clear environmental differences between species pair and non-species pair lakes, my study suggests that a major determinant of the existence of stickleback species pairs is the community of fish present in the lakes and that nesting habitat heterogeneity and its influence on pre-mating reproductive barriers may be important to the persistence of these species pairs. My study provides a baseline to monitor the environments for all known species pair lakes and suggests that the fish assemblage in stickleback lakes may affect resource availability as strongly as the limnological attributes of the lakes themselves although predation may also be an important factor in the evolution of these species pairs.
Biodiversity is of critical importance to the quality of life on Earth. In light of rapidly increasing extinction rates in recent years, understanding threats to biodiversity such as habitat destruction, over-exploitation, and the introduction of invasive species is of utmost importance to conservation efforts. Invasive species, in particular, are a threat of great concern in aquatic environments, due, in part, to their potential role in facilitating introgressive hybridization between closely related species. In recent decades, such a case of hybridization has led to genomic extinction in a benthic-limnetic species pair of threespine stickleback (Gasterosteus aculeatus) in Enos Lake, British Columbia, following the appearance of invasive American signal crayfish (Pacifastacus leniusculus) in this waterbody. In an effort to shed light on the potential role of these crayfish in this loss of diversity, research was conducted using an intact species pair from Paxton Lake, BC to determine if crayfish exert meaningful impacts on sticklebacks through the disruption of i) male stickleback reproductive behaviours and/or ii) juvenile stickleback growth rates. The results of reproductive behaviour trials demonstrated that limnetic male reproductive behaviour frequency was suppressed to a greater degree than that of benthic males in the presence of crayfish. This result suggests that crayfish disruptions may reduce conspecific mating opportunities for limnetic females, thus leading to increases in introgressive hybridization between benthic males and limnetic females. The results of the juvenile growth rate trial, on the other hand, demonstrated that crayfish do not disrupt growth rates of juveniles; however, significantly higher stickleback mortality levels were detected in the presence of crayfish. I conclude that invasive American signal crayfish have likely facilitated introgressive hybridization between the Enos Lake species pair, but other factors may have contributed to this loss of biodiversity. My study highlights the sensitivity of recently differentiated species to disruption by invasive species. By identifying important sources of ecological disruption and significant threats to biodiversity, such studies are critical for guiding conservation efforts in Canada and worldwide.