Status of the relict population of the Critically Endangered Madagascar spider tortoise Pyxis arachnoides

Abstract

The Madagascar spider tortoise Pyxis arachnoides is endemic to the coastal dry forests of south-west Madagascar. In recent years its range has been reduced by c. 71%, with the species now confined to eight fragmented populations occupying a total of 2,464 km 2 . These remaining populations are facing a significant threat of extinction because of habitat destruction and other anthropogenic pressures. We developed methodology for a line transect distance sampling survey and applied it systematically across the species' range. The resulting distance model estimated a mean density of 226.9 tortoises km −2 (95% confidence interval, CI, 168.1-306.3) and a total population of 664,980 (95% CI 492,680-897,550). Fragmentation of the species' range suggests the current population could be , 30% of the historical population. Of the remaining population 73.5% falls within protected areas. However, nine of these 12 protected areas are designated as IUCN category III, V or VI parks, allowing some extractive activities to be undertaken. The most effective strategy for the conservation of P. arachnoides would be to reduce the threats to this species and its habitat, and to develop and expand the current community-based conservation and poverty alleviation programmes in the region.

A novel herpesvirus from a wild-caught Madagascar spider tortoise shows evidence of host-viral coevolution with a duplication event in Durocryptodira

“…Cheloniologists describe current threats to survival including habitat destruction, predation by humans, and collection for the exotic pet trade. 29,30 Detection of a picornavirus from the lung of a spider tortoise has been reported, but otherwise, we found no reports regarding viruses in this species. 20…”

The illegal pet trade is driving Madagascar's ploughshare tortoise to extinction

“…Distance sampling (Buckland et al, 2001) is widely used for monitoring land tortoises (Swann et al, 2002; Leuteritz et al, 2005; Young et al, 2008; Smith et al, 2009; Walker & Rafeliarisoa, 2012) and has been carried out by Durrell Wildlife Conservation Trust periodically since 2005 (with a pilot study in 2003–2004) to estimate ploughshare tortoise densities. Line transects were surveyed in October–April in 2006–2008, 2011–2013 and 2014–2015, between 08.00–11.00 and 15.00–17.00, because tortoises were more active during these cooler hours.…”

“…All four of Madagascar's endemic tortoise species, the radiated tortoise Astrochelys radiata , ploughshare tortoise Astrochelys yniphora , spider tortoise Pyxis arachnoides and flat-tailed tortoise Pyxis planicauda , are listed on Appendix I of CITES (2017) and categorized as Critically Endangered on the IUCN Red List (Leuteritz et al, 2008; Leuteritz & Pedrono, 2008; Leuteritz & Rioux Paquette, 2008; Leuteritz & Walker, 2014). All have been, or are currently, affected by illegal collection from the wild for the international pet trade (O'Brien et al, 2003; Pedrono, 2008; Walker & Rafeliarisoa, 2012).…”

Isolation and characterization of six polymorphic microsatellite loci for the Malagasy spider tortoise, Pyxis arachnoides and cross-amplification in Pyxis planicauda

“…Therefore, while it cannot be discarded that some null alíeles segregate in these taxa, the nature of the current dataset does not allow us determining whether these alíeles' frequencies are of major concern. P. a. brygooi survives in isolated areas of Madagascar and due to the high rate of exploitation of this subspecies, most likely presents much smaller population sizes than the other two subspecies (Pedrono, 2008;Walker, 2010;Walker and Rafeliarisoa, 2012). However, when compared to P. a. arachnoides, P. a. brygooi expected heterozygosity and average number of alíeles per locus do not significantly differ between the two subspecies (/?-valuer: mean number of alíeles ig = 0.75; mean expected heterozygosity t^ = 0.91).…”

“…Furthermore, habitat destruction is contributing to the decline of this species, with the outcome that in many localities the species has almost completely disappeared (Pedrono, 2008;Walker and Rafeliarisoa, 2012). This is especially true for P. a. brygooi, which only survives in remote locations far from human contact (Pedrono, 2008;Walker, 2010).…”