Female secondary coloration in the Mexican boulder spiny lizard is associated with nematode load

Brighter is darker: the Hamilton–Zuk hypothesis revisited in lizards

Several studies of lizards have made an erroneous interpretation of negative relationships between spectral brightness and parasite load, and thus provided misleading support for the Hamilton–Zuk hypothesis (HZH). The HZH predicts that infected hosts will produce poorer sexual ornamentation than uninfected individuals as a result of energetic trade-offs between immune and signalling functions. To test whether there is a negative relationship between spectral brightness and pigment content in the skin of lizards, we used spectrophotometry to quantify the changes in spectral brightness of colour patches of two species after chemically manipulating the contents of orange, yellow and black pigments in skin samples. Carotenoids were identified using high-performance liquid chromatography. In addition, we compared the spectral brightness in the colour patches of live individuals with differential expression of nuptial coloration. Overall, the analyses demonstrated that the more pigmented the colour patch, the darker the spectrum. We provide a comprehensive interpretation of how variation in pigment content affects the spectral brightness of the colour patches of lizards. Furthermore, we review 18 studies of lizards presenting 24 intraspecific tests of the HZH and show that 14 (58%) of the tests do not support the hypothesis.

The evolution of male mate choice and female ornamentation: a review of mathematical models

The evolution of male preferences and of female ornaments in species with traditional sex roles (i.e., polygyny) have been highlighted as areas in need of more active research by an accumulation of recent findings. The theoretical literature on these topics is relatively small and has centered on the evolution of male choice. Mathematical models have emphasized that, under polygyny, the evolution of male preferences faces much greater competition costs than does the evolution of female preferences. We discuss ways in which costly male choice can nonetheless evolve, via (1) direct selection that favors preferences, primarily through mating with highly fecund females, (2) mechanisms that rely on indirect selection, which weakly counters competitive costs of male preferences, and (3) genetic constraints, primarily in the form of pleiotropy of male and female preferences and traits. We also review a variety of mathematical models that have elucidated how costs to male preferences can be avoided. Finally, we turn our attention to the relatively scant theoretical literature on the effects of male mate choice on the evolution of female traits. We emphasize the finding that the presence of male preferences cannot be assumed to lead to the evolution of female ornaments during polygyny, and point out situations where models have elucidated ways in which female ornaments can nevertheless evolve.

Superciliums in white-eared hummingbirds as badges of status signaling dominance

The role of badges as indicators of contest ability has been previously described. In hummingbirds, the exhibition of a badge is expected to save energy expenditure in agonistic interactions and to favor energy intake. Here, we investigate whether variable supercilium size in the white-eared hummingbird has a role in dominance status signaling. Firstly, 45 hummingbird males were captured and their superciliums were photographed to investigate variation in size and any possible allometric relationships. Secondly, 42 male birds were used to analyze whether the supercilium has a role in dominance status signaling in a dyadic contest. We found that supercilium size varied continuously but that despite variability between individuals, there was no relationship between supercilium size and body size. However, our dyad experiment indicated that birds with larger badges were able to make more visits to the feeders than individuals with smaller badges. We suggest a status signaling function of the supercilium.

A structural colour ornament correlates positively with parasite load and body condition in an insular lizard species

Pigment-based ornaments in vertebrates may reflect the body condition or health status of the individual in correlation with environmental stress and hormonal balance. Among the environmental factors shaping sexual colouration, parasitic infections have been stressed as an important evolutionary pressure constraining the maintenance of pigment-based ornaments. However, the honesty of structure-based ornaments in vertebrates is still under debate. Structural UV-biased ornaments in Gallotia lizards were described as a trait used by conspecifics during mate and rival assessment suggesting the reliability of these signals. We investigated the relationship between parasitaemia, body condition and a structural-based ornament present in the cheek of the sexually dichromatic Canarian lacertid Gallotia galloti in a population with an almost 100 % prevalence of haemoparasites. Using spectrophotometric techniques, we found that males with higher values of cheek UV chroma were infected with more haemoparasites. No significant relationship was found between haemoparasite load and body condition. However, males with higher cheek UV chroma showed significantly better body condition. In addition, we found that cheek hue was significantly related to body condition of individuals in both sexes. In males, cheek reflectivity biased towards the UV range was significantly related to better body condition. In females, those individuals with better body condition showed more whitish cheeks with less UV suggesting that cheek hue serves as an intersexual signal for sex recognition. We conclude that the positive relationship between cheek chroma and parasite load in male lizards is compatible with both differential density of melanin and iridophore arrangement in the dermis conveying an individual's ability to cope with environmental stress.

Two new species of Parapharyngodon parasites of Sceloporus pyrocephalus, with a key to the species found in Mexico (Nematoda, Pharyngodonidae)

Two new species of Parapharyngodon collected from the intestine of the Mexican boulder spiny lizard Sceloporuspyrocephalus are described. This study increases to 49 the number of valid species assigned to Parapharyngodon worldwide, 11 of them distributed in Mexico. Males of the two new species share the presence of four pairs of caudal papillae, an anterior echinate cloacal lip and the presence of lateral alae; however, both differ from each other in lateral alae extension and echinate cloacal anterior lip morphology. Females of both species have a prebulbar uterus and eggs shell punctuate with pores, characteristics shared with few other species of Parapharyngodon. Both new species differ from other congeneric species in the papillar arrangement, the anterior cloacal lip morphology, the lateral alae extension and total length/spicule ratio. A taxonomic key for the species of Parapharyngodon distributed in Mexico is provided.

Genetics and evolution of colour patterns in reptiles

The study of coloration in the polyphyletic reptilians has flourished in the last two decades, in particular with respect to the underlying genetics of colour traits, the function of colours in social interactions, and ongoing selection on these traits in the wild. The taxonomic bias, however, is profound: at this level of resolution almost all available information is for diurnal lizards. Therefore, we focus on case studies, for which there are as complete causal sequences of colour evolution as possible, from phenotypic expression of variation in colour, to ongoing selection in the wild. For work prior to 1992 and for a broader coverage of reptilian coloration we refer the readers to Cooper and Greenburg's (Biology of the Reptilia, 1992) review. There are seven major conclusions we would like to emphasise: (a) visual systems in diurnal lizards are broadly conserved but among the wider range of reptiles in general, there is functionally important variation in the number and type of photoreceptors, spectral tuning of photopigments and optical properties of the eye; (b) coloration in reptiles is a function of complex interactions between structural and pigmentary components, with implications for both proximate control and condition dependence of colour expression; (c) studies of colour-variable species have enabled estimates of heritability of colour and colour patterns, which often show a simple Mendelian pattern of inheritance; (d) colour-polymorphic lizard species sometimes, but not always, show striking differences in genetically encoded reproductive tactics and provide useful models for studying the evolution and maintenance of polymorphism; (e) both male and female colours are sometimes, but not always, a significant component of socio-sexual signalling, often based on multiple traits; (f) evidence for effects of hormones and condition on colour expression, and trade-offs with immunocompetence and parasite load, is variable; (g) lizards show fading of colours in response to physiological stress and ageing and are hence likely to be appropriate models for work on the interactions between handicaps, indicator traits, parasitology and immunoecology.

Tail loss compromises immunity in the many-lined skink, Eutropis multifasciata

Tail autotomy incurs energetic costs, and thus, a trade-off in resource allocation may lead to compromised immunity in lizards. We tested the hypothesis that tailless lizards will favor constitutive innate immunity responses over an energetically costly inflammatory response. The influence of fasting and colorful ornamentation was also investigated. We experimentally induced tail autotomy in the lizard Eutropis multifasciata and found that inflammation was suppressed by tail loss, but not further affected by fasting; the suppressive effect of colorful ornamentation was manifested only in males, but not in females. Constitutive innate immunity was not affected by any of these factors. As expected, only costly inflammation was compromised, and a less expensive constitutive innate immunity might be favored as a competent first-line defense during energetically demanding periods. After considering conventional trade-offs among tail regeneration and reproduction, further extending these studies to incorporate disease risk and how this influences escape responses to predators and future reproduction would make worthwhile studies.

Past or present? Relative contributions of developmental and adult conditions to adult immune function and coloration in mallard ducks (Anas platyrhynchos)

Developmental conditions affect adult physiological processes and phenotypic traits, including those associated with both survival and reproduction. Carotenoids are molecules that generate sexually attractive coloration, and these pigments are acquired throughout life and can affect antioxidant capacity and immunocompetence of young and old animals. However, few studies have tracked carotenoid status and condition during development and into adulthood to understand how ontogeny affects later-life health and coloration of both males and females. We reared male and female mallard ducks (Anas platyrhynchos) from hatch to adulthood, measured circulating carotenoid titers and body condition (i.e., size-adjusted body mass) throughout development, and assessed adult immune function and integumentary carotenoid-based beak and foot coloration. We found that adult immune function (wing web swelling response to phytohemagglutinin; PHA) in males was positively correlated with body condition during the growth period of development, rather than adult condition, and similarly that both male and female beak coloration was associated with developmental, rather than adult, body condition. We also found associations between coloration and health during adulthood; males with more carotenoid-rich beaks (a sexually attractive feature) tended to have a more robust adult PHA response and a greater antibody response to a novel antigen, while females with less carotenoid-rich beaks had greater antibody responsiveness at adulthood. In addition, male beak color changed over the course of the 24-h PHA test in proportion to the degree of PHA swelling. However, intensity of foot coloration (a trait of unknown sexual significance) was not associated with any condition, carotenoid, or immune metric for males or females. Taken together, our findings implicate key developmental components to the expression of both survival- and reproduction-related traits at adulthood, but that for a dynamic trait like beak color, there are also important adult conditions that can alter signal expression.