Dissertations / Theses on the topic 'Cryptic variation'

Physiological traits such as standard metabolic rate have been shown to vary up to half an order of magnitude between individuals and species and influence key life history tradeoffs in juvenile salmonids (e.g. smolt timing). The purpose of my thesis research was to examine the relationship between food consumption, dominance and disproportionate feeding on physiological traits and adaptive strategies of juvenile salmonids. Results show that SMR is positively correlated with food consumption and growth in juvenile coho salmon which showed a reduction in SMR under low food and an elevation in SMR under high food (Chapter 2). Comparisons between hatchery and wild juvenile steelhead and coho salmon revealed no difference in Stnadard metabolic rate between wild coho and wild steelhead but a significant difference in the hatchery fish, with hatchery steelhead being higher. In both wild and hatchery populations I found a marked difference in maximal metabolic rate between steelhead and coho, leading to a greater aerobic scope and swim performance in wild steelhead but no difference in the hatchery fish. This result is consistent with a steelhead energy maximizing strategy, habitat partitioning and trade-offs between elevated SMR at higher growth and decreased swim performance. Interestingly, wild steelhead with higher maximum growth, swim performance, and maximum food consumption do not appear to tradeoff increased growth against lower swim performance, as commonly observed for high growth strains. Instead steelhead appear to be trading off higher growth for lower food consumption efficiency; highlighting potential differences in food consumption and digestion strategies as cryptic adaptations that have received little attention. In experiments conducted in semi-natural stream channels, I found that dominant coho salmon were able to achieve higher absolute growth rates compared to smaller subordinates, at high food ration but suffered significantly lower absolute growth at low food ration as larger dominant fish approached the capacity of their habitat (Chapter 4). Overall I demonstrated that the relationship between physiological traits, life history strategy and dominance rank depended on per capita food consumption rates, habitat characteristics (pools vs riffles) and the absolute size of individuals in a dominance hierarchy.

Crypsis can be an important mechanism of predator avoidance for organisms. However, many species exhibit sexual dichromatism, in which the males possess a suite of colorations in order to attract female attention. The resulting differences in crypsis between the males and females can provide insight into the relative strengths of the sexually and naturally selective forces shaping the coloration of the organism, as well as clues regarding potential sensory biases of the selecting sex. In this study, I examine variation in the coloration of four Pacific Northwest populations of the sexually dimorphic and dichromatic polygynous species of jumping spider Habronattus oregonensis and compare the coloration of different body regions of the spiders to their habitats. I also investigate differences in relative size of a male sexual ornament, the enlarged first leg tibia. Field work for this study was conducted in June and July of 2009. The three main foci of this study are 1) to compare the degree of color matching of females and their habitat to the degree of color matching of males and their habitat, evaluating whether sexual selection on males has reduced their degree of crypsis relative to that of females, 2) if there is indeed a difference in crypsis between the sexes, to gauge whether there are similar divergences from crypsis among the populations - both in the quantitative amount of divergences as well as the colorimetric direction of such divergences, and 3) whether there is any variation in sexual ornament size among populations. Male first leg tibia size is a sexual character that is presumably not influenced by habitat coloration; differences in male tibia allometry among populations would provide supporting evidence for the hypothesis that sexual selection is indeed maintaining phenotypic differences among the populations, regardless of habitat location and color. I found a high degree of conformity of hue and chroma between male and female spiders and their habitats, with three notable exceptions. The most extreme difference in coloration between spider and habitat was that of the Gorge and Siskiyou population male anteriors. The anteriors had proportionally less green and more ultraviolet reflectance than their habitat. Second, the Mt. Hood and Tillamook population male abdomens diverged from their habitat in a similar, although less pronounced manner to that of the Gorge and Siskiyou population male anteriors: they had proportionally less green and more UV reflectance. Third, female abdomens of all populations were highly variable in chroma, despite having hues that generally matched their habitat. Tibia area relative to body size of Gorge and Siskiyou population males was significantly smaller than that of Mt. Hood and Tillamook population males. The lower level of background hue matching among males compared to females implies that sexual selection has directly conflicted with natural selection, resulting in impaired crypsis. While the reduced crypsis of the Gorge and Siskiyou population males is centered on their anterior (the primary body region presented to the females during courtship), the deviations from crypsis in the Mt. Hood and Tillamook population males are highest on their abdomen, although the degree of contrast is lower than that of the Gorge and Siskiyou population anteriors. These differences in coloration between the Mt. Hood and Tillamook population male abdomens and their habitats are in the same colorimetric direction as those of the Gorge and Siskiyou population anteriors and their habitat; this may indicate a sensory bias of the females, conserved in all four populations, selecting for male reflectance with a higher UV to green ratio. The fact that Mt. Hood and Tillamook population male abdomens have a more modest reduction in background matching compared to Gorge and Siskiyou population male anteriors may be due to the search methods of flying predators (e.g., spider wasps); the dorsum would presumably be more conspicuous to predators than the anterior, and would thus be subject to more intense selection for crypsis despite sexual selection to the contrary. The variability of abdomen coloration of females of both morphs may indicate that selection for crypsis is less strong among females than among males. One possible reason for this would be if females spent less time in the exposed courtship habitat than males, a conclusion implied by a highly male-skewed sex ratio encountered during field collections. Like the differences in coloration between different males of different populations, the significant differences in male tibia size also imply variability in the intensity of sexual selection. Relative importance of male coloration and tibia size may be weighted differently among populations, operating under similar constraints on reductions in survival accrued by developing these characters. The high degree of variation found among the populations implies that there is a degree of reproductive isolation among the chromatically and morphologically dissimilar populations. However, the similarity of the environments in which the populations existed, the close geographic proximity of some of the dissimilar populations, and the lack of any substantial geographic boundaries between the populations imply that this isolation is not maintained through extrinsic factors. Rather, it would seem that the interpopulational diversity is maintained by sexual selection. However, evidence from morphology and coloration suggest that the generation of this diversity is not evolving exclusively under sexual selection pressure, but rather is constrained to a degree by natural selection.

L’originalité du golfe de Gabès (Sud de la Tunisie) a été reconnue par les malacologistes depuis le19ème siècle mais reste mal définie. Les espèces de cette région présentent des caractères morphologiques qui ont conduit à l’établissement de variétés, sous-espèces et espèces faiblement caractérisées. Certains auteurs les traitent comme des taxons endémiques tandis que d'autres les considèrent comme de simples variants locaux d'espèces à large répartition méditerranéenne. Le manque d’information concernant la valeur taxonomique de ces caractères morphologiques ne permet pas de traiter de façon robuste la question de l’endémisme dans le golfe de Gabès. Le premier objectif est de réviser le statut taxonomique des mollusques du golfe de Gabès en s’appuyant sur une approche de taxonomie moléculaire. La confrontation des différents caractères a permis d’identifier ceux qui discriminent correctement les individus en espèces, d’éliminer à l’inverse ceux qui ne remplissent pas cette fonction et d’en redéfinir de nouveaux. Le deuxième objectif est de relier les particularités faunistiques du Golfe à ses caractéristiques océanographiques et de discuter les phénomènes de spéciation qui pourraient être à l’origine de l’endémisme. Nos analyses ont porté sur six genres: Jujubinus (Trochidae), Diodora (Fissurellidae), Ocinebrina, Muricopsis (Muricidae), Aplus (Buccinidae) et Tritia (Nassariidae). L’approche intégrative utilisée a permis de proposer des hypothèses de délimitation d’espèces que nous avons ensuite confrontées aux données morphologiques et géographiques. Au final, l’endémisme est confirmé dans certains cas mais l’hypothèse qu’une partie des espèces décrites du golfe de Gabès ne sont que des variétés éco phénotypiques est également attestée. Notre approche moléculaire a mis aussi en évidence l’existencede nouvelles espèces et d’espèces cryptiques insoupçonnées dans la Méditerranée. Finalement l’hypothèse que le golfe de Gabès est un centre de spéciation est retenue. Plus de données moléculaires (reliées à des données fossiles) d’autres groupes provenant de différentes localités (spécialement du golfe de Syrte) apparaissent toutefois nécessaires<br>The present Mediterranean marine fauna is the result of a history going back to the Messinian Salinity Crisis, with current biogeographical patterns mostly reflecting Quaternary to modern oceanographic conditions. The Gulf of Gabès, in southern Tunisia, is remarkable for its extreme ecological characteristics that distinguish it from "ambiant" Mediterranean conditions. Starting with the work of malacologists at the turn of the 19th-20th centuries, the molluscs of the Gulf of Gabès have been recognized as exhibiting morphological characters that set them apart from more typical forms that occur in the rest of the Mediterranean. At present, 6% of the species of the overall Gulf of Gabès mollusc fauna are treated as valid local endemics. Using an integrative taxonomy approach, combining molecular and morphological data, the objective of the study is to re-evaluate the status of these Gulf of Gabès local forms: are they valid, endemic species or do they represent ecophenotypic variation? Given the young geological age (6-8 ka) of the Gulf, where would local endemics have originated? The gastropod genera Jujubinus (Trochidae), Diodora (Fissurellidae), Tritia (Nassariidae) Ocinebrina (Muricidae), Muricopsis (Muricidae) and Aplus (Buccinidae) all have in common non-planktotrophic larval development. Our integrative approach confirms the validity of some of the endemic taxa, but also infirm that others are not valid species; molecular data also reveal unsuspected cryptic lineages both within and outside the Gulf. Regarding the question of the origin of the endemic species, various hypotheses have been proposed, one of them being that the Gulf of Gabès is a “speciation factory”. To formally test this hypothesis, more molecular data (coupled with fossil record data) are needed from other species groups and from other localities in the Mediterranean (specifically the Gulf of Syrte)