Age‐dependent genetic effects on a secondary sexual trait in male Alpine ibex,Capra ibex

Abstract

Secondary sexual traits, such as horns in ungulates, may be good indicators of genetic quality because they are costly to develop. Genetic effects on such traits may be revealed by examining correlations between multilocus heterozygosity (MLH) and trait value. Correlations between MLH and fitness traits, termed heterozygosity-fitness correlations (HFC), may reflect inbreeding depression or associative overdominance of neutral microsatellite loci with loci directly affecting fitness traits. We investigated HFCs for horn growth, body mass and faecal counts of nematode eggs in wild Alpine ibex (Capra ibex). We also tested if individual inbreeding coefficients (f') estimated from microsatellite data were more strongly correlated with fitness traits than MLH. MLH was more strongly associated with trait variation than f'. We found HFC for horn growth but not for body mass or faecal counts of nematode eggs. The effect of MLH on horn growth was age-specific. The slope of the correlation between MLH and yearly horn growth changed from negative to positive as males aged, in accordance with the mutation accumulation theory of the evolution of senescence. Our results suggest that the horns of ibex males are an honest signal of genetic quality.

Direct and indirect causal effects of heterozygosity on fitness-related traits in Alpine ibex

“…with high levels of heterozygosity) become big (large body mass) and resistant to parasites (low FEC), and consequently can afford to also grow long horns. This result supports the hypothesis that horn growth in male Alpine ibex is an honest advertisement of individual quality [65], as suggested by von Hardenberg et al [38]. Our final causal model contradicts the hypothesis of a direct relationship between FECs and body mass previously found in the same population by Decristophoris et al [66].…”

“…Even if the current conservation status of Alpine ibex is considered as 'least concern' in the IUCN Red List of threatened species [33], its recent demographic history [34] and its generally low genetic variability [35,36] suggest this species is worth special attention. Inbreeding depression is expected to particularly affect the isolated and recently reintroduced populations founded by few individuals [37], but it probably also affects the original bottlenecked population in Gran Paradiso [38]; in fact, the main genetic bottleneck event suffered by the population at the beginning of the nineteenth century [36] is quite recent in genetic terms, considering the long generation times that characterize this species (about 7-8 years), and the reduced effective population size is expected to be enough for HFCs to arise [12,13] also in the original population. Better knowledge of the effects of inbreeding in Alpine ibex is thus important to understand how long the effects of a bottleneck can last in a long-lived mammal, and for conservation purposes.…”

Age‐ and quality‐dependent DNA methylation correlate with melanin‐based coloration in a wild bird

“…Several studies have established relationships between elaborate sexual traits and heterozygosity (Foerster et al., 2003; von Hardenberg et al., 2007; Pérez‐González, Carranza, Torres‐Porras, & Fernández‐García, 2010) and these associations tend to be strongest at peak reproductive age (Von Hardenberg et al., 2007). However, our study is the first to our knowledge to have explored the covariation between DNA methylation and sexual trait expression and specifically to attribute age‐ and heterozygosity‐dependent CpG methylation patterns to trait expression.…”

“…Sexual traits are often strongly age‐ and condition‐dependent, making them excellent candidates for honest signals that might be used by females to assess male quality; for example, they may carry information about an individual's past and current nutritional status, hormonal status, and/or parasite load (Thompson, Hillgarth, Leu, & McClure, 1997; Ohlsson, Smith, Råberg, & Hasselquist, 2002; Scheuber, Jacot, & Brinkhof, 2003). Furthermore, in many species including birds (Aparicio, Cordero, & Veiga, 2001; Foerster, Delhey, Johnsen, Lifjeld, & Kempenaers, 2003; Ferrer, García‐Navas, Bueno‐Enciso, Sanz, & Ortego, 2015), mammals (von Hardenberg et al., 2007), and fishes (Herdegen, Dudka, & Radwan, 2014), sexual trait expression is associated with genetic quality, as measured by multilocus heterozygosity. Although these associations are as yet poorly understood, a plausible explanation is that they reflect a general tendency for heterozygous individuals to be superior in relation to diverse life history traits (Hansson & Westerberg, 2002) and that heterozygosity influences sexual trait expression indirectly via its effects on body condition.…”

“…Hence, relationships between sexually selected traits and individual quality may vary with age, with the strongest relationships being found during periods of maximal trait expression (Hooper, Tsubaki, & Siva‐Jothy, 1999; Von Hardenberg et al., 2007). Such dynamic patterns of trait expression would not be possible if trait expression was solely under a purely static genetic control; instead epigenetic control mediated by body condition has been proposed as one means of modifying sexual trait expression (Jašarević, Geary, & Rosenfeld, 2012; Valena & Moczek, 2012).…”