Reproduction as a Function of Living Conditions: The Breeding Biology of the Radiated Tortoise (Astrochelys radiata) under Natural and Captive Conditions in Southwest Madagascar
The Radiated Tortoise (Astrochelys radiata) is one of Madagascar's four critically endangered tortoise species that has been heavily impacted by poaching. Despite successful captive breeding programs for this species, within Madagascar and internationally, little information is available detailing their reproductive ecology in the wild. In this study, I compare the characteristics of this species' reproduction and reproductive success in 1) a wild population (WP) within their natural habitat in Tsimanampetsotsa National Park, and 2) a captive population (CP) that is exposed to regional climatic conditions in southwest Madagascar. Breeding activities were seasonal, with egg depositions from February until October and mean (±SD) clutch sizes of 3.4 ± 1.6 eggs (CP) and 2.5 ± 0.5 eggs (WP). I found egg mass to be positively correlated with female body mass, and the CP tortoises were larger than in the WP. Egg masses in the CP (36.6 ± 6.4 g) were higher than in the WP (30.1 ± 4.0 g). Incubation time was between 132 and 271 d for the CP hatchlings, and incubation time in the WP was 210–292 d. Hatchlings from the CP emerged in December and January, whereas emergence was restricted to December in the WP. Hatchling body mass did not differ between the two populations. My results suggest that removing large individuals from wild populations (as a result of poaching pressure to support the local bush meat trade) may compromise the reproductive output and long-term survival of this species in the wild.Abstract
Range map of Astrochelys radiata in southern Madagascar showing distribution areas in 1865, 1975, and 2000 (data from O'Brien, 2002). Survey sites from this study are indicated with stars.
All clutches that produced hatchlings. Clutches from the CP were recorded in 2008 and clutches from the WP in 2009. In the WP, no observations were conducted after June 2009. Hatchlings of the WP were observed in December 2009 while hatching in captivity was observed in December 2008 and January 2009.
Hatchling body mass on the day of birth compared to the time of eclosion. The date of first hatchling observed in each population gives the zero point to which all further hatchlings are referred. Body mass of WP hatchlings decreased significantly with time (r = −0.63, P = 0.03, n = 12), whereas CP hatchlings showed an increasing body mass (r = 0.49, P = 0.04, n = 18). Hatchlings from clutches laid after June 2008 are excluded from the fit line of the CP.
