An unexpected journey: the biogeography and conservation ecology of the trapdoor spider genus Cantuaria Hogg, 1902

Abstract

The genus Cantuaria consists of 42 currently recognised species, all of which are endemic to New Zealand (NZ). Cantuaria spiderlings build their burrows near to their mothers, and usually remain there for life.

Cantuaria’s sedentary life history is at odds with its distribution, which reaches from Stewart Island up to Whanganui. Cantuaria’s sister genus Misgolas Karsch, 1878 is found in Australia. In this thesis, I used a dated multilocus Bayesian phylogeny to reconstruct [1] when the most recent common ancestor (MRCA) of Cantuaria diverged from Misgolas, and [2] the distribution history of Cantuaria within NZ. My results showed that Cantuaria and Misgolas shared a MRCA as recently as 18 million years ago, indicating long distance dispersal in Cantuaria’s biogeographic history. However, there was also evidence to suggest that vicariant geographic barriers interrupt dispersal, as species to the east and west of the Southern Alps share a most recent common ancestor approximately 5-8 million years ago. The genus appears to have originated in the southern part of the South Island, before moving gradually northwards. Cantuaria phylogenies were used to delimit species using the Poisson tree process, and 12 new species are described. Morphology and phylogeny do not concur, and geographic location combined with DNA are the most reliable methods for identifying Cantuaria species.

Due to Cantuaria species’ small populations (defined as a semi-isolated individual or group of individuals) and lack of dispersal ability, I hypothesised that they would be susceptible to habitat loss and disturbance. My research investigated how different types of habitat and disturbance affect Cantuaria population presence/absence. I also assessed the threats that may be facing individual populations. A taxon that is easily susceptible to changing environmental parameters may be less likely to survive and colonise new territory after a long-distance ocean crossing. My results show that Cantuaria, surprisingly, are able to breed and reproduce in a variety of habitat types, but they are found less often in areas with very high rainfall, and in high elevation areas. Some populations appear to contain very few individuals, and may be threatened by habitat destruction. The threats to Cantuaria populations include climate change (which may increase rainfall in some areas) and urbanisation. A meta-analysis of biogeographical research from the last decade for all taxa investigated the factors that may affect a species’ biogeographic history in NZ and found no evidence to suggest that characteristics, such as dispersal ability, affect a species’ biogeographical history over evolutionary time.