Sexual and seasonal differences in the vomeronasal epithelium of the red‐backed salamander (Plethodon cinereus)

Abstract

Sexually dimorphic behaviors often are associated with sexually dimorphic neural structures. Perinatal hormonal levels influence structural sexual dimorphism, and seasonal structural changes also can be the result of seasonal hormonal fluctuations. We compared the volume of vomeronasal organs of male and female red-backed salamanders (Plethodon cinereus) throughout the year. Odorants are delivered to vomeronasal receptors through nasolabial grooves when salamanders touch the bases of these grooves to objects (nose tapping). Males may locate and identify potential mates through nose tapping during the prolonged breeding season that lasts from October through May. We compared vomeronasal organ data through multiple regression by using total body size, sex, and season as variables that may influence vomeronasal organ volume. Gonads also were examined as an indicator of reproductive status. Total body size and sex significantly affect vomeronasal organ volume; as body size increases, so does vomeronasal organ volume, and males have significantly larger vomeronasal organs than females at all times of the year. During the summer, both males and females have larger vomeronasal organs than at any other time of the year. Summer also is a period of intense foraging and the initiation of a new cycle of gametogenesis. Previous studies of circulating hormone levels in amphibians have shown that the initial stages of gametogenesis correspond to a period of low estradiol and testosterone levels but high gonadotropin-releasing hormone levels. The functional significance of sexual and seasonal differences in the vomeronasal organs of P. cinereus may relate to the neurogenesis of specialized receptors for courtship and mating. o 1995 WiIey-Liss, Inc.

The vomeronasal organ of greater bushbabies (Otolemur spp.): Species, sex, and age differences

“…Sexual dimorphism of the VNNE with males > females has been hypothesized to relate to mate-finding behaviors (Dawley & Crowder, 1995) or to polygamous mating strategies (Tai et al, 2004). The results of the present study lend support to either hypothesis in that the genus Otolemur has a dispersed multimale social system in which males have home ranges overlapping those of multiple females (Nash & Harcourt, 1986;Müller & Thalmann, 2000).…”

“…The results of this study suggest greater bushbabies are similar to a number of other vertebrate species in possessing sexually dimorphic VNNE volume (Dawley & Crowder, 1995;Maico et al, 2003;Segovia & Guillamón, 1982;Tai et al, 2004). Sexual dimorphism of the VNNE with males > females has been hypothesized to relate to mate-finding behaviors (Dawley & Crowder, 1995) or to polygamous mating strategies (Tai et al, 2004).…”

“…In many species, volume, cross-sectional area, receptor neuron density, and total number of receptor neurons in the vomeronasal neuroepithelium (VNNE) are greater in males than females (Dawley & Crowder, 1995;Segovia & Guillamón, 1982;Tai et al, 2004), although the reverse is true in some rodents (Maico et al, * To whom correspondence should be addressed. 2003).…”

Seasonal morphometry of the vomeronasal organ in the marsupial mouse, Antechinus subtropicus

“…Neurogenesis of vomeronasal neurons also increases during pregnancy in female mice (Kaba et al, 1988). In some animals, the neural sensory epithelium of the VNO varies seasonally; proliferation being temporally associated with changes in seasonal behaviors (Dawley and Crowder, 1995; Dawley, 1998; Dawley et al, 2000; Kondoh et al, 2012). Male salamanders have significantly larger VNOs than females at all times.…”

“…However, before the breeding period, the size of the VNO increases in both males and females. As salamanders use their VNO to locate potential mates, the increase in size might reflect increased neurogenesis, controlled by gonadal or pituitary hormones (Dawley and Crowder, 1995). In Japanese striped snakes, by contrast, morphological and histological features of the VNO sensory epithelium do not change seasonally, but VNO receptor cell proliferation and turnover appears to increase rapidly during hiberation (Kondoh et al, 2012).…”