Sympatric colour polymorphisms associated with nonrandom gene flow in cichlid fish of Lake Victoria

Colour polymorphisms have fascinated evolutionary ecologists for a long time. Yet, knowledge on the mechanisms that allow their persistence is restricted to a handful of well-studied cases. We studied two species of Lake Victoria cichlid fish, Neochromis omnicaeruleus and Neochromis greenwoodi, exhibiting very similar sex-linked colour polymorphisms. The ecology and behaviour of one of these species is well studied, with colour-based mating and aggression preferences. Here, we ask whether the selection potentially resulting from female and male mating preferences and aggression biases reduces gene flow between the colour morphs and permits differentiation in traits other than colour. Over the past 14 years, the frequencies of colour morphs have somewhat oscillated, but there is no evidence for directional change, suggesting the colour polymorphism is persistent on an ecological timescale. We find limited evidence of ecomorphological differentiation between sympatric ancestral (plain) and derived (blotched) colour morphs. We also find significantly nonrandom genotypic assignment and an excess of linkage disequilibrium in the plain morph, which together with previous information on mating preferences suggests nonrandom mating between colour morphs. This, together with negative frequency-dependent sexual selection, found in previous studies, may facilitate maintenance of these polymorphisms in sympatry

Genetics of male nuptial colour divergence between sympatric sister species of a Lake Victoria cichlid fish

The hypothesis of sympatric speciation by sexual selection has been contentious. Several recent theoretical models of sympatric speciation by disruptive sexual selection were tailored to apply to African cichlids. Most of this work concludes that the genetic architecture of female preference and male trait is a key determinant of the likelihood of disruptive sexual selection to result in speciation. We investigated the genetic architecture controlling male nuptial colouration in a sympatric sibling species pair of cichlid fish from Lake Victoria, which differ conspicuously in male colouration and female mating preferences for these. We estimated that the difference between the species in male nuptial red colouration is controlled by a minimum number of two to four genes with significant epistasis and dominance effects. Yellow colouration appears to be controlled by one gene with complete dominance. The two colours appear to be epistatically linked. Knowledge on how male colouration segregates in hybrid generations and on the number of genes controlling differences between species can help us assess whether assumptions made in simulation models of sympatric speciation by sexual selection are realistic. In the particular case of the two sister species that we studied a small number of genes causing major differences in male colouration may have facilitated the divergence in male colouration associated with speciation.

An empirical examination of the integration of causal attribution and social learning theories in achievement situations

Using path analysis, the present investigation sought to clarify possible operational linkages among constructs from social learning and attribution theories within the context of a self-esteem system. Subjects were 300 undergraduate university students who completed a measure of self-esteem and indicated expectancies for success and minimal goal levels for an experimental task. After completing the task and receiving feedback about their performance, subjects completed causal attribution and self-esteem questionnaires. Results revealed gender differences in the degree and strength of the proposed relations, but not in the mean levels of the variables studied. Results suggested that the integration of social learning and attribution theories within a single conceptual model provides a better understanding of students' behaviors and self-esteem in achievement situations.

Eggshell colour is more strongly affected by maternal identity than by dietary antioxidants in a captive poultry system

1.Biologists have long puzzled over the apparent conspicuousness of blue-green eggshell coloration in birds. One candidate explanation is the sexual signalling hypothesis that the blue-green colour of eggshells can reveal an intrinsic aspect of females' physiological quality, with only high-quality females having sufficient antioxidant capacity to pigment their eggs with large amounts of biliverdin. Subsequent work has argued instead that eggshell colour might signal condition-dependent traits based on diet. 2.Using Araucana chickens that lay blue-green eggs, we explored (i) whether high levels of dietary antioxidants yield eggshells with greater blue-green reflectance, (ii) whether females differ from one another in eggshell coloration despite standardized environments, diets and rearing conditions, and (iii) the relative strength with which diet vs. female identity affects eggshell coloration. 3.We reared birds to maturity and then placed them on either a high- or low-antioxidant diet, differing fourfold in Vitamin E acetate and Vitamin A retinol. After 8 weeks, the treatments were reversed, such that females laid eggs on both diets in an order-balanced design. We measured the reflectance spectra of 545 eggs from 25 females. 4.Diet had a very limited effect on eggshell spectral reflectance, but individual females differed strongly and consistently from one another, despite having been reared under uniform conditions. However, predictions from avian visual modelling suggest that most of the egg colour differences between females, and nearly all of the differences between diets, are unlikely to be visually discriminable. 5.Our data suggest that eggshell reflectance spectra may carry information on intrinsic properties of the female that laid the eggs, but the utility of this coloration as a signal to conspecifics in this species may be limited by the sensitivity of a receiver to detect it.

Plato and Frankfurt: Two Theories of the Relations Between Love and Living Well

This thesis provides a comparison of the ideas of caring and love as they appear in the works of Plato and Frankfurt. Frankfurt, a contemporary philosopher, maintains that an individual arrives at the most meaningful life through understanding what it is that heor she cares about the most. Interestingly, the instances of eros in Plato's Symposium and Phaedrus resonate with this idea. We see throughout these erotic dialogues similarities to Frankfurt's notions of care and love.Throughout his many works, Frankfurt provides us with several distinct features of care and love. This thesis offers an in depth discussion of each of these features andalso provides commentary from other contemporary philosophers who are familiar with Frankfurt's work. In addition, this thesis applies these features of care and love to Plato's erotic dialogues, and emphasizes areas in which Plato and Frankfurt agree and those inwhich they disagree. In essence, it becomes apparent that while there are many similarities between the ideas of these two prominent thinkers, Plato and Frankfurt do not agree about what constitutes the best human life. Plato maintains that the best life is onespent dedicated to philosophy and in pursuit of the 'good'. Frankfurt, on the other hand,imposes no such limitations on what we should consider the best life because people are likely to have different life experiences that lead them to care about and love different things. Instead he suggests that the best or most meaningful human life is one in which a person spends his or her life caring about the things he or she does, indeed, care aboutand loving those things he or she does, indeed, love.