Introduction

Wild populations of Kuroiwa's ground gecko, Goniurosaurus kuroiwae, have declined because of habitat loss caused by development, predation by alien species such as mongoose, Urva auropunctata, and illegal collection (Toda and Tanaka, 2017). The species is currently listed as “vulnerable” on the IUCN Red List of Threatened Species (Kidera and Ota, 2017) and is in CITES Appendix III (CITES, 2023). Conservation guidelines advocate ex situ methods such as captive breeding to supplement wild populations temporarily, which may be crucial for species preservation (Ministry of the Environment, Government of Japan, 2011). A thorough understanding of reproductive behaviors, including mating, is fundamental for the efficient implementation of captive breeding programs; however, no previous studies on the breeding behavior of G. kuroiwae exist. This species is nocturnal and solitary, complicating observing breeding behavior in situ. This study was conducted to observe and quantify the mating behaviors of G. kuroiwae in captivity to improve the understanding of its reproductive biology to inform and improve captive breeding techniques.

Materials and Methods

Experimental conditions and behavioral observations

Each gecko was kept in a separate plastic container (21.5×36.5×15.0 cm) containing peat moss, red ball soil, a plastic shelter, and a water dish. Rearing conditions were maintained at 18–31°C and >80% humidity; under a 10L:14D photoperiod. Every two days, geckos were fed crickets dusted with vitamin supplements. For mating trials, the geckos were placed in larger containers (34.0×43.0×28.0 cm) containing peat moss and red ball soil. For each trial, one male and female among the five captured individuals were randomly selected and were simultaneously placed together in a breeding container at 21.5–29.8°C. Mating behavior was observed between May and September. Four combinations of male-female pairs were tested during the trials (Table 1). Each trial lasted 16 hours, from 1800 to 1000 h, with 40 lx illumination. Behaviors were recorded using a digital video camera (Hero7 Black, GoPro Inc.) and were categorized into precopulatory, copulatory, and postcopulatory stages. In total, 15 trials were conducted.

Table 1.

Pairing of male and female Kuroiwa's ground geckos (Goniurosaurus kuroiwae) during mating trials. Black circles indicate the successful insertion of the male hemipenis into the female cloaca.

Results and Discussion

Insertion of the male genitalia into the female cloaca (defined as mating success) was observed in 12 (80%) of the 15 trials (Table 1; Fig. 1). The male and female precopulatory, copulatory, and postcopulatory behaviors are described in Fig. 1, Table 2; photographs of the behaviors are shown in Fig. 2.

The first step in precopulatory behavior is the sex identification of the mating partner. Previous studies indicate that in many gecko species, mating behavior is typically initiated by males (Brillet, 1993; Regalado, 2003; Todd, 2005). In Eublepharis macularius, Hemidactylus mabouia, and Sphaerodactylus vincentii, males lick females to obtain chemical signals for sex identification (Regalado, 2003; Marcum et al., 2008; Mason and Parker, 2010); however, in the present study, G. kuroiwae males licked females in only five cases (33%), suggesting the possibility that they recognize sex via other cues than non-volatile chemicals on the body surface of females. Additionally, males frequently initiated neck biting (67%; 10 cases) rather than tail biting, and neck biting was observed in all successful matings. This behavior, also observed in other geckos (e.g., He. mabouia and Hoplodactylus maculatus) (Regalado, 2003; Todd, 2005), has been described as a mechanism for female restraint during copulation. Therefore, neck biting by males likely contributes to successful copulation and mating success in G. kuroiwae. Furthermore, females approached males in five cases (33%), all of which resulted in successful copulation. This behavior, coupled with females raising their tails, would be a reliable indicator of female readiness for copulation. Although the time between introduction to the container and the onset of interaction varied in the present study (147–38, 117 s), mating was successful even in the cases where the outset of interaction was delayed. This suggests that if mating behavior does not begin immediately, cohabitation at least overnight is required for captive breeding of G. kuroiwae.

Fig. 1.

Mating behavioral sequence in Kuroiwa's ground gecko (Goniurosaurus kuroiwae) were categorized into precopulatory, copulatory, and postcopulatory patterns for both sexes. The behaviors are presented in the chronological order as displayed during mating.

Among copulatory behaviors, successful mating occurred in all cases that progressed to the “copulatory position.” Additionally, “gaping mouth” and “contortion” were observed, which, to our knowledge, have not been reported in other geckos. Among postcopulatory behaviors, licking of genitalia, as observed after copulation in the present study, may be a further indicator of ejaculation; similar behaviors have been observed in various gecko species (e.g., E. macularius, Thecadactylus rapicauda, He. maculatus, and He. mabouia) (Regalado, 2003; Todd, 2005; Quesnel, 2006; Huang, 2013). Further studies with larger sample sizes are needed to evaluate the interspecific differences in the reproductive behavior and the functional significance of licking of genitalia between this and the other gecko species.

Table 2.

Definitions and quantitative data on mating behaviors observed in Kuroiwa's ground geckos (Goniurosaurus kuroiwae) presented in chronological order.

Fig. 2.

Photographs depicting mating behaviors of Kuroiwa's ground gecko (Goniurosaurus kuroiwae): (A) male licks female, (B) male bites female, except on the neck, (C) male bites female neck and female raises its tail, (D) copulatory position, (E) gaping mouth, and (F) male licks its own genitalia.

This is the first report on the mating behavior of G. kuroiwae in captivity. The observed behavioral patterns and quantitative data across precopulatory, copulatory, and postcopulatory stages serve as indicators of mating success and provide valuable insights for informing captive breeding programs and improving the mating success rates. However, due to the small number of individuals used, these observations unlikely cover the entire repertoire of reproductive behavior of this species. Future studies with a larger number of individuals and populations are warranted.