Comb Size Research Articles

Is sexual ornamentation an honest signal of male quality in the Chinese grouse (Tetrastes sewerzowi)?

We examined the variation in sexual ornamentation of male Chinese grouse (Tetrastes sewerzowi) in the Gansu Province, China, seeking to identify factors involved in whether ornament size and brightness are honest signals of male quality. Compared to unmated males, mated males had significantly larger and redder combs and, although they did not have significantly larger territories, they defended them more vigorously. Mated males had significantly higher blood carotenoid and testosterone levels, significantly better body condition, and significantly lower parasite loads than unmated males. Our findings are thus consistent with the hypothesis that comb size and color are honest signals of better male quality in the grouse, mediated through lower parasite loads and/or higher testosterone levels.

Size and symmetry of sex combs were not related to male mating success inDrosophila melanogasterreared at different temperatures

AbstractTemperature is one of the most important climatic factors that may influence different traits (morphological, physiological or behavioral) inDrosophila. In this study, we examined the effects of two developmental temperatures (18°Cand 25°C) on the size and the symmetry of sex combs (a male sexual trait) and their importance for male mating success inDrosophila melanogaster. However, the number of sex comb teeth (“size”) and its difference between right and left legs (“symmetry”) were relevant neither to male mating success nor to the growth temperatures.

Fighting behaviour as a correlate of male mating success in black grouse Tetrao tetrix

Fighting is a fundamental determinant of male fitness in species where females prefer socially dominant males as mates or where dominants can prevent subordinates from mating. This in turn can lead to the evolution of honest inter- and intra-sexual cues of male dominance. Fighting as a behaviour comprises both fighting rate (number of fights per unit of time) and fighting performance (success in winning fights), but it is not always clear which of these components are important for female choice and how they link to signals of male quality. To quantify the relative importance of fighting as a cue for females, we recorded detailed behavioural data from male black grouse Tetrao tetrix at leks. We explored the relationship between phenotypic traits (body mass, eye comb size, tail (lyre) length and blue chroma colouration) and fighting performance and rates and how these were related to male mating success. In older males' pairwise fights, winners had lower blue chroma than losers, but there were no differences in other morphological traits. In yearlings, no morphological trait predicted success in pairwise contests. Both fighting rate and performance were positively related to the number of copulations acquired by a male; however, when controlled for lek centrality, fighting performance and not fighting rate was significantly related to mating success. Our results indicate that females may be using components of fighting behaviour as cues for mate choice.

Qualitative Traits Characterization of Yoruba and Fulani Ecotype Indigenous Chickens in Derived Savannah Zone of Nigeria

4 Abstract: Qualitative traits characteristics of indigenous Chickens in derived savannah Zone of Nigeria were studied. A total of two thousand and forty one (2,041) indigenous chickens comprising 1274 Yoruba Ecotype Chickens (YEC) and 767 Fulani Ecotype Chickens (FEC) were sampled for the study. Traits studied included Sex, Comb Size, Wattle Size, Comb Type, Ear lobe Colour, Feather Structure, Plumage and Comb Colour. The result indicated that female chickens dominated the two Ecotypes with 52.04% in YEC and 52.28% in FEC. Highest percentage of Large Comb Size was observed for male chicken in both ecotypes: 67.57% in YEC and 71.32% in FEC. Three types of wattle size were observed in the two populations (Small, Medium and Large). Proportion of Large Wattle size favoured male chickens (YEC: 51.13%, FEC: 49.38%) in both populations. Three different types of comb (Single, Rose and Pea) with Single Comb type dominant over others (94.29% in YEC and 80.44% in FEC). Three colour patterns of ear lobe were observed in YEC with White Ear Lobe (69.07%) dominated the population while five colour patterns were observed in FEC with Red Ear lobe (74.97%) dominated. Three feather structure (Normal, Frizzled and Naked Neck) pattern were observed in the two populations, Normal type had the highest percentage (YEC: 83.99%, FEC: 83.05%). Plumage colour varied widely, six different types were observed in YEC and mixed colour had the highest percentage (31.4%) followed by dominant black (25.69%) while Eight different types of plumage colour were observed in FEC in which black colour (31.55%) had the highest percentage. The study revealed a wide variation in some of the traits, therefore future study can be concentrated on selection for qualitative traits of interest.

Environmental conditions influence red grouse ornamentation at a population level

Theory suggests that condition-dependent sexual displays should be more weakly expressed under adverse conditions than under more favourable ones. Here, we tested this hypothesis in wild red grouse Lagopus lagopus scoticus using a data set of nearly 1500 individuals from nine populations over 8 years, covering varying environmental conditions. We analysed whether male and female ornament expression (i.e. comb size) in a given site and year varied with various indices of environmental conditions: population density, Trichostrongylus tenuis nematode infection at the population level, and climate conditions [measured as winter North Atlantic oscillation (NAO) index]. We found that average comb size in males, but not in females, negatively correlated with population density, parasite infection levels, and winter NAO index. Furthermore, the coefficient of variation (CV) of comb size was higher in females than in males. CVs in both males and females were not clearly associated with the studied environmental variables. Our results support the idea that the expression of condition-dependent sexual traits should be lower under more stressful environmental conditions, but only in males. We discuss the potential reasons behind the effect of environmental conditions on secondary sexual traits, and why these effects differ between sexes. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107, 788–798.

Comb: An important reliable visual ornamental trait for selection in chickens

Many cues for selection exist in poultry breeding, giving important insights into the future selection of elite progeny. Among these cues, the comb is an important reliable parameter for selection within variety or breed. The development of the comb is associated with hormone levels in the body which affect both productive and reproductive parameters. Comb affects the mating behaviour of birds and may be used as an indicator for selection by examining its impact on performance. Strong selection for increased comb size has been shown not to affect male mortality but is linked to increased female mortality. The production traits of layers have a positive correlation with comb size. The following paper provides a review of the comb as an important ornamental trait, including its morphology, development, use as a selection tool and the effect of comb size on productive and reproductive traits.

Social context decouples the relationship between a sexual ornament and testosterone levels in a male wild bird

In order to maximise fitness individuals should adjust their level of signalling according to their surrounding social environment. However, field experiments showing such adjustment of current signalling associated to changes in social context are lacking. Here, we manipulated levels of male aggressive- and dominance-related displays in a wild bird in our treated area by increasing testosterone levels using implants in a subset of males. We then compared the expression of sexual signals (i.e. comb size) between non-treated red grouse Lagopus lagopus scoticus males from control and treatment areas. We further explored the potential endocrinological mechanism linking social environment and signal expression by analysing testosterone levels in all males. Our treatment successfully increased overall aggressive- and dominance-related behaviours in the treatment area. Furthermore, testosterone-implanted birds increased their comb size as repeatedly shown in previous studies in male red grouse. Interestingly, untreated males living in the treatment area decreased their comb size, whilst increasing testosterone levels. Since comb size is a signal of dominance, untreated males from the treatment area may have perceived themselves as subordinate individuals and decreased their signalling levels to avoid confrontations with testosterone-treated, dominant individuals. In conclusion, our findings show that social context has the potential to regulate sexual signalling and testosterone levels. Our results highlight the role of social context when exploring the link between testosterone and behaviour, as it may reverse the relationship between both traits. Our results suggest that social context affects signalling and testosterone independently.

Age-specific oxidative status and the expression of pre- and postcopulatory sexually selected traits in male red junglefowl, Gallus gallus.

Oxidative stress is emerging as a key factor underpinning life history and the expression of sexually selected traits. Resolving the role of oxidative stress in life history and sexual selection requires a pluralistic approach, which investigates how age affects the relationship between oxidative status (i.e., antioxidants and oxidative damage) and the multiple traits contributing to variation in reproductive success. Here, we investigate the relationship between oxidative status and the expression of multiple sexually selected traits in two-age classes of male red junglefowl, Gallus gallus, a species which displays marked male reproductive senescence. We found that, irrespective of male age, both male social status and comb size were strongly associated with plasma oxidative status, and there was a nonsignificant tendency for sperm motility to be associated with seminal oxidative status. Importantly, however, patterns of plasma and seminal antioxidant levels differed markedly in young and old males. While seminal antioxidants increased with plasma antioxidants in young males, the level of seminal antioxidants remained low and was independent of plasma levels in old males. In addition, old males also accumulated more oxidative damage in their sperm DNA. These results suggest that antioxidant allocation across different reproductive traits and somatic maintenance might change drastically as males age, leading to age-specific patterns of antioxidant investment.

Comb size and color relate to sperm quality: a test of the phenotype-linked fertility hypothesis

In many avian species, males display dramatic and conspicuous ornaments that serve as honest signals of quality to females. The phenotype-linked fertility hypothesis suggests that the honesty of these signals may be maintained through a link with fertility. Indeed, in some recent studies, bright coloration has been linked with better fertility and also indicates semen characteristics that influence fertility, such as sperm performance. However, most of these studies were performed on species with ornamental feather coloration, in which the ornament is produced months prior to reproduction. We tested the phenotype-linked fertility hypothesis in the domestic rooster, a species where comb characteristics fluctuate on a short-term basis according to environmental and physiological conditions and thus may serve as immediate signals of quality to hens. We examined the relationships of comb size and color with measures of sperm quality, including concentration, mobility, and viability. We found that comb size was inversely correlated, whereas comb color was positively correlated with sperm viability. Thus, males with the smallest reddest combs had the highest percentage of viable sperm. Our finding that comb color signals better quality sperm supports the phenotype-linked fertility hypothesis. However, the negative relationship between comb size and sperm viability indicates that females who choose larger ornaments also choose males with lower fertility, a counterintuitive behavior in terms of the phenotype-linked fertility hypothesis. To understand these signals in an adaptive context, it is important to determine how each individual comb characteristic is interpreted and utilized by females during mate choice.

Optical contrastivity of complicated materials: finite layered structures

We define the intrinsic optical contrastivity of a complicated layered structure as the relative total gap taken inside the total internal reflection region over a chosen range of frequencies. The notion introduced for ordered 1D systems retains its meaning for 2D and 3D ordered optical systems, as well as for disordered structures. The parametric maps of contrastivity and sensitivity are calculated for 1D comb matrices based on glass, silicon, and microporous silicon with various fillings, comb sizes, and densities of a gaseous filling. The existence of areas on a parametric map which are highly sensitive to deviations in the contrastivity is shown for different materials. In the case of a gaseous filling of voids between the matrix material layers, the areas of a very high sensitivity are also found.

Developmental instability as phenodeviance in a secondary sexual trait increases sharply with thermal stress

We test for effects of thermal stress applied to pupal flies from Noumea (New Caledonia) and Taipei (Taiwan) on developmental instability (DI) in the male sex comb of Drosophila bipectinata, as well as on pre-adult survivorship and adult body size. The temperature treatments were Low (25 °C), High (29 °C) and Variable (18 h at 29 °C, 6 h at 34 °C). Although the Variable treatment reduced survivorship and body size, absolute comb size and fluctuating asymmetry generally were invariant across treatments. In contrast, comb phenodeviance increased with stress in both populations. Phenodeviance in one comb segment (C2) increased sharply with stress, whereas phenodeviance in a second major segment (C1) also increased with stress but only in Noumea flies. A major conclusion is that phenodeviations induced in a secondary sexual trait reflect the developmental environment that also damages fitness components, a foundation stone of the hypothesis that expressions of DI reveal phenotypic quality in sexual selection.

The relationship between the comb and social behaviour in laying hens

The question of whether attributes of the combs of laying hens have any consistent relationship with dominance behaviour has yet to be answered unequivocally. This study sought to address this by investigating whether a relationship existed between the competitive ability of hens within stable groups and the size or colour of their combs. Pullets ( n = 120, Hy-line ® Variety Brown) were allocated randomly to eight groups of 15 hens for 32 weeks. Over this period the length and height of each hen's comb was measured regularly to estimate the total comb area and hens were weighed. In weeks 3–10 the aggressive interactions between hens in each group were observed to calculate a behavioural dominance score (David's score) for each hen. This score was based on the outcome of agonistic interactions with other group members; and accounts for the relative strengths of all opponents. Thus dominance scores reflected the competitive ability of hens from their overall within-group fighting success. The luminance, purity and dominant wavelength of the colour of each hen's comb was measured in week 27 using a telespectroradiometer. Hens with higher dominance scores had larger combs than those with lower dominance scores (gradient of slope = 0.008 ± 0.002, P < 0.001); this relationship was consistent across the experiment. There was no association between body weight and dominance score but there was a significant inverse relationship between dominance score and the dominant wavelength of the comb (gradient of slope = −0.067 ± 0.023, P < 0.01). This indicated that hens with combs perceived by humans as more yellow-red than pure red were generally more successful competitors. Further research is required to ascertain whether or not hens utilise this information on comb size and the underexplored area of comb colour to assess the competitive ability of their opponents.

Sex combs, allometry, and asymmetry in Drosophila

There has been recent debate about the expected allometry of sexually-selected traits. Although sexually-selected traits exhibit a diversity of allometric patterns, signalling characters are frequently positively allometric. By contrast, insect genitalia tend to be negatively allometric, although the allometry of nongenital sexually-selected characters in insects is largely unknown (with some notable exceptions). It has also been suggested that there should be a negative association between the asymmetry and size of bilaterally-paired, sexually-selected traits, although this claim is controversial. We assessed the allometry and asymmetry (fluctuating asymmetry, FA) of a nongenital contact‐courtship structure, the sex comb, in replicate populations of three species of Drosophila (we also measured wing FA). Sex combs are sexually-selected characters used to grasp the female’s abdomen and genitalia and to spread her wings prior to and during copulation. Although species differed in the size of the sex combs, all combs were positively allometric, and comb allometry did not generally differ significantly between species or populations. Comb and wing asymmetry did vary across species, although not across populations of the same species. However, FA was trait specific and was never negatively associated with trait size. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 923‐934. ADDITIONAL KEYWORDS: developmental stability ‐ Diptera ‐ D. melanogaster ‐ D. pseudoobscura ‐ D. simulans ‐ fluctuating asymmetry ‐ scaling.

Condition- and parasite-dependent expression of a male-like trait in a female bird

In many species, females display brightly coloured and elaborate traits similar to those that males use in intra- and inter-sexual selection processes. These female characters are sometimes related to fitness, and might function as secondary sexual characteristics that have evolved through sexual selection. Here, we used descriptive data from 674 females in 10 populations and an experimental removal of Trichostrongylus tenuis parasites in four populations, to examine the effects of season, age, condition, and parasites on the size of supra-orbital combs displayed by female red grouse Lagopus lagopus scoticus. We found that comb size (i) was greater during the breeding than the non-breeding season, (ii) was greater in adult than in young females, (iii) was positively correlated with body condition, and (iv) negatively correlated with parasite abundance. Experimentally, we showed that comb size increased proportionally to the number of worms removed after parasite dosing. Our findings provide a better understanding of proximate mechanisms behind the expression of a male-like trait in females, and we discuss its possible function as a female ornament.

Metal Combs Used for Hair Separation in Scalp Surgery

Many head and neck surgery procedures are performed in the scalp area. However, during these procedures, hair usually interferes with the visualization of the surgical area, reducing the surgeons’ comfort. Other technical difficulties originating from hair include suturing and hemostasis problems, infection, and bad scar formation. Removal of the hair in the incisional area seems to be a promising method, yet it remains an inefficient solution, especially for patients with long hair. Removal of hair from a wide area around the planned incision also is not desired because it usually takes a long time for that scalp area to be covered with hair again, and most of these patients remain worried or annoyed until that time. To provide better exposure of the incisional area, certain methods are described in the literature, including petrolatum or ointment usage to keep hair flat [1], grouping of hair with rubber materials [2], and use of hair clips [3]. However, none of these applications has reached sufficiently wide acceptance to be implemented as a standard method. A new and simple technique for hair separation to increase surgical comfort has been designed. With this method, two or three pieces of medium-sized metal hair combs are used (Fig. 1). The combs are reusable after sterilization in an autoclave. The number and the size of the hair combs can be arranged according to the dimension of the surgical field and the needs of the surgeon. Thus, the hair surrounding the incisional area can be grouped in two to four opposite directions and held in place with the help of the hair combs (Fig. 2). The teeth of the combs secure the hair in place, and the combs can be left in position by themselves, diminishing the need for assistance. Nevertheless, an assistant also can hold the combs and apply gentle pressure on them for even better exposure. Hair constitutes a major obstacle in scalp surgery. It blocks visualization of the surgical field; makes it difficult to locate the suture thread, complicating the suturing process; and gets into the suture line, increasing infection risk, all of which contribute to an increase in the overall duration of the intervention. The hair gel or ointment used to keep hair flat must be carefully removed at the end of the procedure. Otherwise, it gives discomfort to the patient and blocks hair follicles, which can cause infection or hair loss. Application and removal of hair gel are time-consuming procedures, and the assistance they can offer during surgery is limited. Rubber bands and hair clips also are cheap and useful tools for hair partition, but their use is time consuming as well, and although grouped together, hair can still get between the surgical instruments and the surgical field. The aforementioned tools also are subject to frequent loosening during the procedure. Yet another drawback is the small but annoying pain they can provoke when they are removed from the hair postoperatively. The metal hair combs described in this report are designed to overcome these problems. They offer a practical approach that can effectively simplify and accelerate the procedure, enable the surgeon to work alone without any need for assistance, and improve the postoperative comfort of the patient. B. Ersoy (&) H. Şirinoglu Department of Plastic, Reconstructive and Aesthetic Surgery, Marmara University School of Medicine, Tophanelioglu Cad. No:13-15, Altunizade, 81190 Istanbul, Turkey e-mail: bubu77@gmail.com

Differential condition dependence among morphological traits inferred from responses to heat stress is predicted by sexual selection theory

Secondary sexual traits that are condition-dependent are expected to reveal the physiological state and/or genetic quality of individuals, and therefore, should more often be found to be under sexual selection than (1) secondary sexual traits not currently condition-dependent, and (2) nonsecondary sexual traits. In the present study, we contrasted the degree of condition dependence in three morphological traits of male Drosophila bipectinata: two secondary sexual traits (distinct components of the sex comb), one of which significantly predicts mating success in nature (segment 2), whereas the other does not (segment 1), and a nonsecondary sexual trait (sternopleural bristle number). As predicted, comb segment 2 decreased significantly in size, in response to increasing temperature during development, whereas comb segment 1 and sternopleural bristle number either did not change significantly, or increased with increasing temperature. These results support the hypothesis that condition-dependence, inferred from stress-induced reductions in trait expression, engenders a trait to sexual selection. Small-combed genotypes did not exhibit disproportionate reductions in larva-to-adult survivorship and adult body size compared to large-combed genotypes, suggesting that comb size does not reveal genotypic quality, at least as revealed by sensitivity in body size and juvenile survivorship to thermal stress.

Testing the interactive effects of testosterone and parasites on carotenoid‐based ornamentation in a wild bird

Testosterone underlies the expression of most secondary sexual traits, playing a key role in sexual selection. However, high levels might be associated with physiological costs, such as immunosuppression. Immunostimulant carotenoids underpin the expression of many red-yellow ornaments, but are regulated by testosterone and constrained by parasites. We manipulated testosterone and nematode burdens in red grouse (Lagopus lagopus scoticus) in two populations to tease apart their effects on carotenoid levels, ornament size and colouration in three time-step periods. We found no evidence for interactive effects of testosterone and parasites on ornament size and colouration. We showed that ornament colouration was testosterone-driven. However, parasites decreased comb size with a time delay and testosterone increased carotenoid levels in one of the populations. This suggests that environmental context plays a key role in determining how individuals resolve the trade-off between allocating carotenoids for ornamental coloration or for self-maintenance needs. Our study advocates that adequately testing the mechanisms behind the production or maintenance of secondary sexual characters has to take into account the dynamics of sexual trait expression and their environmental context.

Does male secondary sexual trait size reveal fertilization efficiency in Australian Drosophila bipectinata Duda (Diptera: Drosophilidae)?

Males developing relatively large, costly sexually selected traits may be of superior body condition compared to small-ornamented males. Thus, males developing the largest secondary sexual trait in a given environment may also be able to augment their investment into ejaculate quality, and fertilize a larger proportion of a female's eggs. We tested the prediction that the degree of expression of a condition-dependent secondary sexual trait, the male sex comb, in a Cape Tribulation (northeastern Australia) population of Drosophila bipectinata Duda, reveals male ability to fertilize eggs in the absence of sperm competition. This test permitted us also to evaluate whether pre-copulatory sexual selection and fertilization efficiency might act additively to influence male reproductive success because a previous study of the same population demonstrated a positive association between comb size and copulation probability. The results obtained indicate that, although genotypes developing smaller sex combs collectively had a significantly higher rate of insemination failure compared to larger comb genotypes, the hatch rate and the number of eggs laid by females inseminated by the two genotypic categories were not statistically different. The results fail to support the prediction that comb size reveals noncompetitive fertilization efficiency of males in this Australian population. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 406–413.

Comb size as an indicator of reproductive traits in acclimatize white Leghorn cockerels: Improvement in reproductive traits breeding values associated with selecting according to comb size

This study was conducted at the Poultry Farm / Animal Resources Department, College of Agriculture, Baghdad University, and over the period from 15/10/2004 until 30/9/2005, used 24 sires ,144 dam and 217 progeny . The aim of this study was to obtain genetic improvement of certain reproductive traits (semen volume, packet cell volume, sperms movement scales, fertility, hatchability, alkaline phosphatase, total protein and body weight) for white Leghorn by indirect selection according to comb size using traits breeding values that obtained by animal model program . Results obtained showed there were wide variance in traits means ( expressived as standard deviation) that referred to take advantage of this traits in reproductive indirect selection programs especially movement scales , fertility and hatchability. Results referred also that there were genetic improvement in some of reproductive traits [expressed as significant (p< 0.05) raise breeding values means]. There were significant genetic improvement (p< 0.05) take place in most of studied traits in progeny stock because of elite sires selected dependence comb size, that emboldening to use comb size as an indicator in selection programs . Depressions in standard deviation of breeding values were occurred when indirect selection processes, that to be necessary of using large stock . The results supported used comb size for cock’s reproductive traits improvement in progeny flocks.

Hygienic behavior of the stingless bee Plebeia remota (Holmberg, 1903) (Apidae, Meliponini)

We investigated hygienic behavior in 10 colonies of Plebeia remota, using the pin-killed method. After 24 h the bees had removed a mean of 69.6% of the dead brood. After 48 h, the bees had removed a mean of 96.4% of the dead brood. No significant correlation was found between the size of the brood comb and the number of dead pupae removed, and there was no apparent effect of the origin and the condition of the colony on the hygienic behavior of the bees. Plebeia remota has an efficiency of hygienic behavior superior to that of three of the other four stingless bee species studied until now.