Maternal basking regime has complex implications for birthdate and offspring phenotype in a nocturnally foraging, viviparous gecko

Abstract

Maternal basking regime can affect gestation length in viviparous squamates, but effects on offspring phenotype in species with extended pregnancies and ability to delay the birth season are unclear. We investigated the effects of three maternal basking regimes on maternal thermoregulation, gestation length, pregnancy outcome and offspring phenotype in the gecko Woodworthia 'Otago/ Southland'. This long-lived (30+ years), nocturnal forager has field pregnancies lasting up to 14 months, with fully developed offspring maintained in utero over winter. Within regimes, we also compared outcomes for spontaneous (early) deliveries with those from induced (late) deliveries to test the 'adaptive prolongation of pregnancy' hypothesis. Although a cool regime significantly extended gestation, the effect was reduced by increased maternal basking, and embryonic development under the cool regime was just as successful. Offspring from spontaneous births (but not induced births) were smaller and grew more slowly when from the cool regime. However, induced offspring did not differ in consistent ways from those delivered spontaneously and offspring from all groups had high viability, similar use of warm retreat sites and similar sprint speeds. Thus, consistent evidence for adaptive prolongation of pregnancy was lacking. Unusually for squamates, pregnant females can begin vitellogenesis before giving birth, and a profound drop in maternal body temperature near the end of pregnancy (∼6.3°C, confirmed under the warm regime) may assist survival of embryos in utero. Female lizards that maintain fully developed embryos in utero have the potential to make complex trade-offs among birthdate, offspring phenotype and future reproduction.

Sexual Dimorphism of Digit‐Length Ratio in a Viviparous Lizard: Influence of Age, but not Preservation State or Sex of Interuterine Twin

“…Sprint speed at 2–3 months of age for most of the young juveniles (n = 46) was reported in Cree and Hare (b). In brief, the juveniles were held for 3 days without food, then for 2–3 h in an incubator at 25°C.…”

“…Wild females in the Macraes population reproduce biennially and can live an estimated 30 years or more, with maturity in females being reached at about 8 years (Sheehan et al, ; Cree and Hare, ). Even under favorable conditions in captivity, the fastest‐growing individuals take 3–4 years to reach maturity, and gestation length, which is temperature‐dependent, can last 5 months or more (Cree and Hare, b and unpubl.). Nationally, the species’ conservation status is “At Risk‐Declining” (Hitchmough et al, ).…”

“…The 58 juveniles studied here (34 males and 24 females) originated from a separate group of adult females that were captured during early pregnancy in October 2007 and 2008. These females were individually housed to investigate the influence of maternal basking opportunity on pregnancy outcomes and offspring quality (Cree and Hare, b). Briefly, females were exposed to simulated summer air temperatures (15°C during the day and 12°C at night) and photoperiod (15:9 L:D; with dawn and dusk ramps in temperature and lighting levels).…”

“…When heat lamps were on, geckos could bask at their daytime preferred temperature (∼28°C; Rock et al, ) or remain at temperatures as low as room temperature. Although three maternal basking regimes were used (heat lamps on for 8 h day −1 for either 7 day week −1 , 5 day week −1 or 3.5 day week −1, equivalent to 56, 40, or 28 h of basking opportunity per week), sample sizes of offspring were not sufficient to discriminate sexes by basking regime, and we focus here solely on differences between sexes (both sexes were produced from all regimes; Cree and Hare, b). Neonates (either spontaneously delivered or induced following injection of arginine vasotocin; Cree and Hare, b) were marked by toe‐clip, housed in groups of four and maintained on an intermediate basking regime (40 h week −1 ).…”

“…The relationship between digit‐length ratio in the freshly euthanized juveniles and their prior performance (maximum speed) was examined. Offspring speed is influenced by maternal identity and number of pauses, but not by offspring size or maternal basking regime (Cree and Hare, b and unpubl. obs.).…”