Variability of tail length in hybrids of the Japanese macaque (Macaca fuscata) and the Taiwanese macaque (Macaca cyclopis)

Abstract

In primates, tail length is subject to wide variation, and the tail may even be absent. Tail length varies greatly between each species group of the genus Macaca, which is explained by climatic factors and/or phylogeographic history. Here, tail length variability was studied in hybrids of the Japanese (M. fuscata) and Taiwanese (Macaca cyclopis) macaque, with various degrees of hybridization being evaluated through autosomal allele typing. Relative tail length (percent of crown-rump length) correlated well with the number of caudal vertebrae. Length profiles of caudal vertebrae of hybrids and parent species revealed a common pattern: the length of several proximal-most vertebrae do not differ greatly; then from the third or fourth vertebra, the length rapidly increases and peaks at around the fifth to seventh vertebra; then the length plateaus for several vertebrae and finally shows a gentle decrease. As the number of caudal vertebrae and relative tail length increase, peak vertebral length and lengths of proximal vertebrae also increase, except that of the first vertebra, which only shows a slight increase. Peak vertebral length and the number of caudal vertebrae explained 92 % of the variance in the relative tail length of hybrids. Relative tail length correlated considerably well with the degree of hybridization, with no significant deviation from the regression line being observed. Thus, neither significant heterosis nor hybrid depression occurred.

Maxillary sinus variation in hybrid macaques: implications for the genetic basis of craniofacial pneumatization

“…In 2003, the Wakayama prefectural government initiated an eradication programme to eliminate Taiwanese macaques and their hybrids from the region to prevent genetic introgression and its impact on the ecosystem. Since then, more than 300 individuals have been eliminated with the support of the Ministry of the Environment of the Government of Japan (Ohsawa et al ., ; Hamada et al ., ). The members of the Working Group of Wakayama Taiwanese Macaque, Primate Society of Japan, and Primate Research Institute of Kyoto University have been investigating the ecology, morphology, genetics, physiology, and pathology of the hybrid population (Kawamoto, ; Ohsawa et al ., ; Hamada et al ., ).…”

“…Since then, more than 300 individuals have been eliminated with the support of the Ministry of the Environment of the Government of Japan (Ohsawa et al ., ; Hamada et al ., ). The members of the Working Group of Wakayama Taiwanese Macaque, Primate Society of Japan, and Primate Research Institute of Kyoto University have been investigating the ecology, morphology, genetics, physiology, and pathology of the hybrid population (Kawamoto, ; Ohsawa et al ., ; Hamada et al ., ). These studies aimed to help the extermination process of the remaining non‐native and hybrid individuals in Wakayama, and also aimed to evaluate the influence of alien invasion and hybridization on the indigenous ecosystems and biodiversity.…”

“…The specimens derived from Oike area that were used in this study were from individuals captured between 2003 and 2006 (for details see Hamada et al ., ).…”

“…Thus, the degree(s) of hybridization (DH) was estimated by direct counting of codominant alleles at four genetic loci: three are autosomal blood protein loci (transferrin, adenosine deaminase, and NADH‐dependent diaphorase) and one is an autosomal single nucleotide polymorphism on the fifth intron of the NRAMP1 region (Nozawa et al ., , ; Kawamoto, ; Hamada et al ., ). Each locus was genotyped using the diagnostic alleles of Japanese and Taiwanese macaque, and the DH was represented as nine grades, from 0/8 to 8/8, based on the number of Japanese macaque type alleles (Table ; Hamada et al ., ). The F1 generation would be expected to present heterogeneous alleles and 4/8 DH, although post‐F1 generations could also possibly show 4/8 DH.…”

Postsacral Vertebral Morphology in Relation to Tail Length Among Primates and Other Mammals

“…Though shorter‐tailed mammals may possess the same number of proximal postsacral vertebrae as mammals with longer tails (e.g., Macaca , Table ), the summed length of craniocaudally shorter vertebrae produces an absolutely shorter proximal tail region. Consequently, the proximal tail region of a longer‐tailed mammal can theoretically achieve a greater arc of flexion than that of a shorter‐tailed mammal (Ward, ; Shapiro and Simons, ; contra Hamada et al, ), suggesting that tail length reduction is associated with decreased proximal tail flexibility.…”