The natural history and ecology of melanism in red wolf and coyote populations of the southeastern United States – evidence for Gloger’s rule

Abstract

Background Gloger’s rule postulates that animals should be darker colored in warm and humid regions where dense vegetation and dark environments are common. Although rare in Canis populations, melanism in wolves is more common in North America than other regions globally and is believed to follow Gloger’s rule. In the temperate forests of the southeastern United States, historical records of red wolf (Canis rufus) and coyote (Canis latrans) populations document a consistent presence of melanism. Today, the melanistic phenotype is extinct in red wolves while occurring in coyotes and red wolf-coyote hybrids who occupy the red wolf's historical range. To assess if Gloger’s rule could explain the occurrence and maintenance of melanistic phenotypes in Canis taxa, we investigated differences in morphology, habitat selection, and survival associated with pelage color using body measurements, GPS tracking data, and long-term capture-mark-recapture and radio-telemetry data collected on coyotes and hybrids across the southeastern United States. Results We found no correlation between morphometrics and pelage color for Canis taxa. However, we observed that melanistic coyotes and hybrids experienced greater annual survival than did their gray conspecifics. Furthermore, we observed that melanistic coyotes maintained larger home ranges and exhibited greater selection for areas with dense canopy cover and wetlands than did gray coyotes. Conclusions In the southeastern United States, pelage color influenced habitat selection by coyotes and annual survival of coyotes and hybrids providing evidence that Gloger’s rule is applicable to canids inhabiting regions with dense canopy cover and wetlands. Greater annual survival rates observed in melanistic Canis may be attributed to better concealment in areas with dense canopy cover such as coastal bottomland forests. We suggest that the larger home range sizes of melanistic coyotes may reflect the trade-off of reduced foraging efficiency in lower quality wetland habitat for improved survival. Larger home ranges and differential use of land cover by melanistic coyotes may facilitate weak assortative mating in eastern coyote populations, in which melanistic animals may have lower success of finding compatible mates in comparison to gray conspecifics. We offer that our observations provide a partial explanation for why melanism is relatively low (< 10%) but consistent within coyote populations throughout southeastern parts of their range.

Heterozygosity is low where rare color variants in wild carnivores prevail

“…Melanism has reached frequencies of approximately 50% in these areas, which is unlikely to relate to a concealment advantage (Dekker, 2009 ) or reproductive fitness (Stahler et al., 2013 ), and may instead be the result of genetic drift. The binary appearance of melanistic wolves, as well as coyote, across their range (Hinton et al., 2022 ) supports the notion that neutral, rather than selective, processes are at play. In European badgers Meles meles , a population has recently established in central Norway where leucism now seems abundant, likely as a result of a founder effect (Hofmeester et al., 2021 ).…”

Isabelline coloration: a heretofore unrecognized chromatic aberration in bighorn sheep

“…affected by these chromatic aberrations, and the subtle differences that exist among isabellinistic, leucistic, and albinistic individuals. Minor distinctions are difficult to ascertain in field settings (Holl and Bleich 1983;Bleich 1998), but also when aberrantly colored individuals are encountered during aerial surveys (Bleich 2017a), or through the use of remote cameras, upon which more and more investigators rely, yet may not have the resolution to detect subtle differences (Parker et al 2020). Moreover, reliability of classifications has been shown to increase with the number of discriminating characteristics (Smith 1988).…”

Historic samples reveal loss of wild genotype through domestic chicken introgression during the Anthropocene

“…While the discovery of domestication-specific alleles suggests continual and fairly strong reproductive isolation between chickens and wild junglefowl [14,15], signatures of genomic admixture indicate that the domestic-wild divide has not always been absolute: several studies have established gene flow from domestic chickens into wild junglefowl, although the opposite scenario remains less well documented [16][17][18][19][20][21]. Although domestic introgression can be beneficial to populations of a wild ancestral species [22,23], preserving wild genotypes of important human domesticates is generally regarded as crucial to preclude sweeps of genomic homogenization and/or a loss of the full range of wild-type genetic diversity [24,25]. Variation within the ancestral population is capable to confer advantages to the domestic population [26].…”