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1.  Basal superoxide as a sex-specific immune constraint 
Biology Letters  2011;7(6):906-908.
There is increasing evidence that reactive oxygen species (ROS), a group of unstable and highly reactive chemical molecules, play a key role in regulating and maintaining life-history trade-offs. Upregulation of ROS in association with immune activation is costly because it may result in an imbalance between pro- and antioxidants and, hence, oxidative damage. Previous research aimed at quantifying this cost has mostly focused on changes in the pro-/antioxidant balance subsequent to an immune response. Here, we test the hypothesis that systemic ROS may constrain immune activation. We show that systemic, pre-challenge superoxide (SO) levels are negatively related to the strength of the subsequent immune response towards the mitogen phytohaemagglutinin in male, but not female painted dragon lizards (Ctenophorus pictus). We therefore suggest that systemic SO constrains immune activation in painted dragon males. We speculate that this may be due to sex-specific selection pressures on immune investment.
doi:10.1098/rsbl.2011.0350
PMCID: PMC3210656  PMID: 21632618
reactive oxygen species; immunity; Ctenophorus pictus; phytohaemagglutinin
2.  Reduced opsin gene expression in a cave-dwelling fish 
Biology Letters  2009;6(1):98-101.
Regressive evolution of structures associated with vision in cave-dwelling organisms is the focus of intense research. Most work has focused on differences between extreme visual phenotypes: sighted, surface animals and their completely blind, cave-dwelling counterparts. We suggest that troglodytic systems, comprising multiple populations that vary along a gradient of visual function, may prove critical in understanding the mechanisms underlying initial regression in visual pathways. Gene expression assays of natural and laboratory-reared populations of the Atlantic molly (Poecilia mexicana) revealed reduced opsin expression in cave-dwelling populations compared with surface-dwelling conspecifics. Our results suggest that the reduction in opsin expression in cave-dwelling populations is not phenotypically plastic but reflects a hardwired system not rescued by exposure to light during retinal ontogeny. Changes in opsin gene expression may consequently represent a first evolutionary step in the regression of eyes in cave organisms.
doi:10.1098/rsbl.2009.0549
PMCID: PMC2817247  PMID: 19740890
regressive evolution; vision; qPCR; Poecilia mexicana; Poeciliidae
3.  Does a predatory insect contribute to the divergence between cave- and surface-adapted fish populations? 
Biology Letters  2009;5(4):506-509.
Immigrant inviability, where individuals from foreign, ecologically divergent habitats are less likely to survive, can restrict gene flow among diverging populations and result in speciation. I investigated whether a predatory aquatic insect (Belostoma sp.) selects against migrants between cave and surface populations of a fish (Poecilia mexicana). Cavefish were more susceptible to attacks in the light, whereas surface fish were more susceptible in darkness. Environmentally dependent susceptibility to attacks may thus contribute to genetic and phenotypic differentiation between the populations. This study highlights how predation—in this case in conjunction with differences in other environmental factors—can be an important driver in speciation.
doi:10.1098/rsbl.2009.0272
PMCID: PMC2781934  PMID: 19443506
ecological speciation; immigrant inviability; local adaptation; predator–prey interaction; reproductive barriers
4.  Does divergence in female mate choice affect male size distributions in two cave fish populations? 
Biology Letters  2008;4(5):452-454.
Sexual selection by female choice can maintain male traits that are counter selected by natural selection. Alteration of the potential for sexual selection can thus lead to shifts in the expression of male traits. We investigated female mate choice for large male body size in a fish (Poecilia mexicana) that, besides surface streams, also inhabits two caves. All four populations investigated, exhibited an ancestral visual preference for large males. However, only one of the cave populations also expressed this female preference in darkness. Hence, the lack of expression of female preference in darkness in the other cave population leads to relaxation of sexual selection for large male body size. While P. mexicana populations with size-specific female mate choice are characterized by a pronounced male size variation, the absence of female choice in one cave coincides with the absence of large bodied males in that population. Our results suggest that population differences in the potential for sexual selection may affect male trait variation.
doi:10.1098/rsbl.2008.0259
PMCID: PMC2610082  PMID: 18559308
non-visual mate choice; sensory shift; sexual selection; size variation; Poecilia mexicana (Poeciliidae)
5.  Costly steroids: egg testosterone modulates nestling metabolic rate in the zebra finch 
Biology Letters  2007;3(4):408-410.
The transfer of non-genetic resources from mother to the offspring often has considerable consequences for offspring performance. In birds, maternally derived hormones are known to influence a variety of morphological, physiological and behavioural traits in the chick. So far, the range of these hormonal effects involves benefits in terms of enhanced growth and competitive ability as well as costs in terms of immunosuppression. However, since yolk hormones can enhance growth and begging activity, high levels of these hormones may also involve energetic costs. Here, we show experimentally that elevated levels of prenatal testosterone increase resting metabolic rate in nestling zebra finches (Taeniopygia guttata). Surprisingly, however, elevation of prenatal testosterone did not result in higher growth rates and, thus, differences in resting metabolism do not seem to be linked to nestling growth. We conclude that apart from immunosuppressive effects, high levels of egg steroids may also entail costs in terms of increased energy expenditure.
doi:10.1098/rsbl.2007.0127
PMCID: PMC2390662  PMID: 17456447
maternal hormones; maternal effects; testosterone; metabolism; Taeniopygia guttata
6.  Parasites in sexual and asexual mollies (Poecilia, Poeciliidae, Teleostei): a case for the Red Queen? 
Biology Letters  2005;1(2):166-168.
The maintenance of sexual reproduction in the face of its supposed costs is a major paradox in evolutionary biology. The Red Queen hypothesis, which states that sex is an adaptation to fast-evolving parasites, is currently one of the most recognized explanations for the ubiquity of sex and predicts that asexual lineages should suffer from a higher parasite load if they coexist with closely related sexuals. We tested this prediction using four populations of the sexual fish species Poecilia latipinna and its asexual relative Poecilia formosa. Contrary to expectation, no differences in parasite load could be detected between the two species.
doi:10.1098/rsbl.2005.0305
PMCID: PMC1626213  PMID: 17148156
maintenance of sex; parasites; gynogenesis; parasitic theory of sex

Results 1-6 (6)