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1.  Dietary carotenoid availability, sexual signalling and functional fertility in sticklebacks 
Biology Letters  2009;6(2):191-193.
In species where males express carotenoid-based sexual signals, more intensely coloured males may be signalling their enhanced ability to combat oxidative stress. This may include mitigating deleterious oxidative damage to their sperm, and so be directly related to their functional fertility. Using a split-clutch in vitro fertilization technique and dietary carotenoid manipulation, we demonstrate that in non-competitive fertilization assays, male three-spined sticklebacks (Gasterosteus aculeatus) that are fed higher (but biologically relevant) levels of carotenoids had a significantly increased fertilization success, irrespective of maternal carotenoid intake. Furthermore, within diet groups, a male's fertilization success was positively related to the expression of his carotenoid-based nuptial coloration, with more intensely coloured males having higher functional fertility. These data provide, to our knowledge, the first demonstration that dietary access to carotenoids influences fertilization success, and suggest that females could use a male's nuptial coloration as an indicator of his functional fertility.
doi:10.1098/rsbl.2009.0815
PMCID: PMC2865065  PMID: 19923137
fertility; carotenoid coloration; antioxidants; oxidative stress
2.  Availability of non-carotenoid antioxidants affects the expression of a carotenoid-based sexual ornament 
Biology Letters  2007;3(4):353-356.
Carotenoids are responsible for much of the yellow, orange and red pigmentation in the animal kingdom, and the importance of such coloration as an honest signal of individual quality has received widespread attention. In particular, owing to the multiple roles of carotenoids as pigments, antioxidants and immunostimulants, carotenoid-based coloration has been suggested to advertise an individual's antioxidant or immune defence capacity. However, it has recently been argued that carotenoid-based signals may in fact be advertising the availability of different antioxidants, many of which (including various vitamins, antioxidant enzymes and minerals) are colourless and so would be uninformative as components of a visual signal, yet often have greater biological activity than carotenoids. We tested this hypothesis by feeding male sticklebacks (Gasterosteus aculeatus) a diet containing a fixed level of carotenoids and either low or high, but biologically realistic levels of the colourless antioxidant vitamins C and E. High-antioxidant diet males produced significantly more intensely coloured (but not larger) carotenoid-based regions of nuptial coloration and were preferred over size-matched males of the opposite diet treatment in mate-choice trials. Furthermore, there were positive correlations between an individual's somatic antioxidant activity and signal intensity. Our data suggest that carotenoid-based ornaments may honestly signal an individual's availability of non-carotenoid antioxidants, allowing females to make adaptive mate-choice decisions.
doi:10.1098/rsbl.2007.0072
PMCID: PMC2390655  PMID: 17472903
α-tocopherol; ascorbic acid; oxidative stress; sexual signalling
3.  Green swordtails alter their age at maturation in response to the population level of male ornamentation 
Biology Letters  2007;3(2):144-146.
Effects of the social environment on age at sexual maturation are assumed to require direct interactions, such as suppression of subordinates through aggression from dominants. Using green swordtails (Xiphophorus helleri), we demonstrate for the first time that females and males adjust their age at maturation in response to visual cues of male sexual ornamentation in the current environment: females matured earlier, whereas males matured later if all the mature males seen had large ornaments. Thus, age at maturation shifted in accordance with the perceived quality of mates (females) or mating competitors (males), demonstrating a capability to use visual cues from the environment to strategically adjust rates of sexual development.
doi:10.1098/rsbl.2006.0608
PMCID: PMC2375941  PMID: 17301010
life-history strategy; local mate competition; phenotypic plasticity; sexual maturation; social environment
4.  Effect of growth compensation on subsequent physical fitness in green swordtails Xiphophorus helleri 
Biology Letters  2005;2(1):39-42.
Early environmental conditions have been suggested to influence subsequent locomotor performance in a range of species, but most measurements have been of initial (baseline) performance. By manipulating early growth trajectories in green swordtail fish, we show that males that underwent compensatory growth as juveniles had a similar baseline swimming endurance when mature adults to ad libitum fed controls. However, they had a reduced capacity to increase endurance with training, which is more likely to relate to Darwinian fitness. Compensatory growth may thus result in important locomotor costs later in life.
doi:10.1098/rsbl.2005.0414
PMCID: PMC1617196  PMID: 17148321
growth rate; exercise; endurance; resource allocation; swimming performance

Results 1-4 (4)