Suzanne M. Gray
PhD Candidate
Behavioural Ecology Research Group
Department of Biological Sciences
Simon Fraser University
Email: smgray@sfu.ca
CV PUBLICATIONS FIELDWORK PHOTOS
Research Interests
One of my main research interests is understanding how diversity evolves and is maintained in nature. More specifically, I am interested in asking questions about the interaction of organisms and the visual environment in which they live. In the future I would like to incorporate these ecological and evolutionary questions into a conservation program aimed at preserving diversity.
PhD Research
Both natural and sexual selection are thought to be important forces in the maintenance of male colour polymorphism. I am trying to test whether selection is influenced by a heterogeneous light environment, thereby maintaining diversity within populations. I use Telmatherina sarasinorum, an endemic fish from Lake Matano, an ancient Sulawesi lake, that has at least five male colour morphs (Fig.1), to test the hypothesis that in alternate habitats different colour males are favoured by sexual selection. Within-habitat diversity may be influenced by conspecific cannibalsim and sneaking. There are two major spawning habitats for this species: shallow beach sites and deeper sites with overhanging roots (Fig.2). I have found that blue males are more frequent and have higher pairing success with females than yellow males in the beach sites and yellow males are predominant and have higher pairing success in the deeper sites. Preliminary light measurements taken in each habitat and colour measurements of each morph indicate that blue fish should be more conspicuous in the shallow habitats whereas yellow males should stand out more against the openwater background of the deeper sites. Several measurements of reproductive success suggest that the most conspicuous morph in a given habitat is the most successful, at least in preliminary analyses. These findings support a role for sexual selection in maintaining colour polymorphism in this species, although natural selection through cannibalistic egg predation may also be involved and is being investigated. (Co-Supervisors Lawrence M. Dill and Jeffrey S. McKinnon)
Blue Blue-Yellow Yellow Grey Grey-Yellow
Fig. 1: Telmatherina sarasinorum (Atheriniformes: Actinopterygii: Telmatherinidae) male colour morphs collected from Lake Matano, Sulawesi, Indonesia.
a) b)
Fig. 2: Two spawning habitats of T. sarasinorum in Lake Matano: a) beach site, b) roots site.
MSc Research
My Masters research focused on testing how resource competition generates diversifying selection that results in adaptive divergence (i.e. ecological character displacement or ECD). I quantified an association between phenotypic and ecological divergence between two similar small fishes, brook (Culaea inconstans) and ninespine (Pungitius pungitius) sticklebacks (Fig.3), in replicate northern Ontario lakes, Canada. The two species partition resources and habitat where they coexist, and brooks that coexist with ninespines are more benthically specialized in body form and diet than brooks from local allopatric populations. I tested various explanations for this pattern. First, I tested the prediction that interspecific competition declines with increased divergence using a manipulative field experiment. I used enclosures placed in a lake to compare short-term fitness (growth) of sympatric (post-displacement) and allopatric (pre-displacement) brook forms in the presence and absence of ninespines. Brooks grew less in the presence versus absence of ninespines, indicating that interspecific competition occurred. As expected, allopatric brooks had lower growth than sympatric brooks when ninespines were present. This result suggests that ecological character displacement has occurred. I also addressed several of the alternative hypotheses that could explain the pattern of devergence: Chance is unlikely to have been the primary cause because divergence is replicated in three separate populations. Preliminary comparisons indicate that resource availability and a variety of abiotic ecological conditions are generally similar between sympatric and allopatric sites, and so do not readily account for the divergence. Biased colonization or extinction is less likely to account for the divergence because character values in sympatry tend to exceed those in allopatry, as expected if they have repeatedly evolved under diversifying selection. Recent studies have also demonstrated that these two species compete, and that competitive effects are more severe for allopatric compared to sympatric brook forms, as predicted if divergence reflects the ghost of competition past. Ongoing studies indicate heritable variation in this system. My results suggest that even small amounts of character shifts can influence competition and hence relative fitness, further implicating a role for ECD in the evolution of biodiversity. (NOTE: All work was done with Beren W. Robinson at the University of Guelph).
a) b)
Fig. 3: a) Brook Stickleback (Culaea inconstans) and b) Ninespine stickleback (Pungitius pungitius) both collected from Rozon Lake, Ontario, Canada and stained with Alizarin red.