The Comb (October 2012)
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Brightness is the maximum intensity value divided by , saturation is the difference between the maximum and minimum intensity values divided by the maximum intensity value, and hue is the difference between the 2 lowest intensity values divided by the maximum intensity value and expressed in degrees 0— Hue, saturation, and brightness were averaged for all 3 pixel points measured for each comb. Mobility measures therefore had to be corrected for the influences of sperm concentration before analyses, and we did this using the residuals of the regression described above.
Because sperm viability is calculated as a percentage, sperm viability data were arcsine transformed. Sperm concentration and the residual sperm mobility values were normally distributed and required no further transformation. To reduce the number of comparisons conducted, both the comb color measurements and the comb size measurements were condensed using separate principal components PCs analyses, resulting in a single PC each for comb color and comb size. Hue and saturation loaded positively, whereas brightness loaded negatively for measurements taken on both occasions For weeks 1 and 2, respectively: A single component for each week was labeled PC1 size and was used as our assessment of comb size.
The relationship between comb size PC1 size and color PC1 color was examined using a simple regression during both weeks of data collection. For data collected during week 1, the relationships of PC1 color and PC1 size with sperm concentration, viability, and mobility were analyzed using simple regressions. To correct for the large number of comparisons conducted during this week a total of 6 , we utilized the Benjamini—Hochberg correction, which controls the false discovery rate Benjamini and Hochberg ; Waite and Campbell For data collected during week 2, we only analyzed the relationships between variables found to be significantly related during week 1 to minimize the number of comparisons made.
Because only 2 comparisons were made during week 2, no correction was employed for those data.
Comb color was inversely correlated with comb size during both weeks of experimentation Figure 1 , week 1: Comb size, represented as the first PC including comb height, length, and area, was inversely correlated with comb color, represented as the first PC incorporating hue, saturation, and brightness of the comb. Data represented here are those collected during week 1.
Relationships of sperm viability, expressed as the percentage of live sperm in a count sample, with A and C comb size and B and D comb color during weeks 1 and 2 of data collection. Comb color was positively correlated with sperm viability during both weeks.
Comb size was negatively correlated with sperm viability, but this relationship was only significant during week 1. Due to the lack of significant relationships between these variables, similar analyses were not conducted for week 2 data. Comb size and color were significant predictors of sperm viability in male broiler breeder chickens. Roosters with smaller redder combs had the highest percentage of viable sperm.
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We originally predicted that both comb size and comb color would correlate positively with measures of sperm quality. This was based on the finding that broiler breeder roosters with wider combs produced sperm that were better able to reach and hydrolyze the perivitelline membrane of the ovum McGary et al.
If these sexually selected ornaments are honest signals of fertility, we would expect that they would be positively correlated with measures of sperm quality. The fact that comb size and comb color were inversely correlated with one another, however, made it impossible for both to correlate positively with our measures of sperm quality. Here, we show that both comb size and color can be used to predict sperm viability, though the relationships are opposite in direction, with comb size relating negatively and comb color relating positively to sperm viability.
The negative correlation of comb size with sperm viability contradicts other studies in which comb size related positively with measures of sperm function in other chicken strains Gebriel et al. This relationship supports the findings of a study by Froman et al. Because dominant roosters have significantly larger combs Graves et al. It is possible that this negative relationship is mediated by an indirect physiological or behavioral factor.
For example, when comb sizes of white leghorn roosters were increased over generations via artificial selection, a decrease in testes mass, the sizes of other secondary sexual characters, and overall viability were observed, suggesting a potential trade-off between sexual traits von Schantz et al. Perhaps, energy utilization for maintaining comb size and other related sexual behaviors limits reserves available to maintain sperm quality. Alternatively, the effect we saw could be directly mediated by local hormonal influences in the testes. Comb size is strictly testosterone dependent reviewed in Owens and Short , resulting from the local production of intracellular fluid by fibroblasts in the comb Hardesty Although testosterone is necessary for processes of sperm maturation, pharmacological levels of androgens in humans resulted in lower sperm quality Torres-Caleja et al.
The findings that dominant males another testosterone-dependent trait have lower sperm quality Froman et al. To our knowledge, though, the relationship between circulating testosterone and sperm quality has not been examined in birds.
Comb color was positively related to sperm viability for both weeks of the study. The physiological link between comb color and sperm viability, however, is unclear. The deep red color of the rooster wattle has been thought to result from the influx of blood hemoglobin in particular into the highly vascularized dermal layer of the skin Stettenheim Carotenoids, pigments responsible for many of the red, yellow, and orange colors in nature, have also been isolated from the comb of the domestic chicken Czeczuga ; however, the relative contributions of heme and carotenoids to variation in comb color among roosters remain controversial McGraw and Klasing Both carotenoids and hemoglobin have demonstrated antioxidant properties Burton ; Chew ; Gabbianelli et al.
Indeed, such a model concerning ornamentation and sperm function has been proposed by Blount et al. Both comb size and color were related to sperm viability but neither were significantly correlated with sperm concentration or mobility except for a negative relationship between comb size and sperm mobility that was no longer significant following statistical correction. The reasoning for the relationship with sperm viability but not the other measures of sperm quality remains unknown.
However, it is not surprising that all quality measures do not vary in a similar manner because different physiological mechanisms underlie variation in each quality measure. However, each measure has been shown to correlate with fertility in the domestic chicken viability and mobility: Cooper and Rowell , reviewed in Wilson et al.
To correct for the large number of comparisons conducted during this week a total of 6 , we utilized the Benjamini—Hochberg correction, which controls the false discovery rate Benjamini and Hochberg ; Waite and Campbell Effect of androgenic anabolic steroids on sperm quality and serum hormone levels in adult male bodybuilders. View the latest posts on the BMC Series blog homepage. In addition, to date, no study has examined the relationship between comb color and characteristics of sperm quality in any species or strain. Our finding that comb color signals better quality sperm supports the phenotype-linked fertility hypothesis. In his phenotype-linked fertility hypothesis, Sheldon suggested that the honesty of avian sexual signals may be maintained by a link between a male's sexual display and his functional fertility. Thus, males with the smallest reddest combs had the highest percentage of viable sperm.
The question remains what these relationships of comb size and color with sperm function really mean in an adaptive context. The phenotype-linked fertility hypothesis suggests a link between a male secondary sexual trait and the functional ability of his sperm Sheldon If females were choosing males that had smaller combs, then this would fit very well with Sheldon's hypothesis, however, in the chicken system, when a preference is documented, that preference is usually for larger combs Zuk, Johnson, et al. This would mean that females are choosing males with lower quality sperm when they choose based on this sexual signal.
These adaptive questions concerning the relationship between sperm function and comb size may become clearer when we consider the negative relationship we saw between comb size and color as well as the strong and persistent positively relationship between comb color and sperm viability. I scraped up as much as possible and kept going. I put in a queen excluder in August because there was capped brood in the first super.
Then in late August, I noticed comb on the excluder. Had I known what would happen, I would have and should have taken out the excluder then. Instead, today I found a huge mess I would never have imagined. I first noticed the comb on the excluder at the end of August.
Highlights of the BMC-series: October 2012
What a mess it became! When I pried off the excluder, it broke open the comb between the brood chamber and the excluder, spilling honey everywhere and opening brood cells on top of the frames. While I was cleaning up as best I could, the bees in the supers had started crawling out, so they were all over the ground and on the outside of the hive and no amount of smoke would get them to go back in so we could reassemble the hive without lots of squished bees.
Within a short time, the entire front of the hive was completely coated with bees. I thought when the sun went down, they would make their way in, but it was the same in the morning.
The Comb Oct 2012
I suited back up to see what was happening as soon as it was light enough to see. Comb size and color relate to sperm quality: Abstract In many avian species, males display dramatic and conspicuous ornaments that serve as honest signals of quality to females. For permissions, please e-mail: Email alerts New issue alert. Receive exclusive offers and updates from Oxford Academic. Related articles in Web of Science Google Scholar. Citing articles via Web of Science Gene expression shifts in yellow-bellied marmots prior to natal dispersal.
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