Exploratory phylogenetic and biogeographic analyses within three land-snail families in southeastern-most Madagascar

Abstract

For Madagascan vicariance biogeography and phylogeny-based conservation, four land snail groups have been predicted as most readily informative: Acavidae, Boucardicus (Cyclophoridae), Reticulapex (Charopidae), and Streptaxidae. Acavids have been evaluated in a previous paper; this paper uses recently described taxa from three mountains in southeastern Madagascar to evaluate the other three groups, based on shell and reproductive characters. Phylogenetic analyses, using appropriate outgroups, were performed on all 17 Boucardicus (31 characters, 120 states), all nine Reticulapex (21 characters, 53 states), and all 15 streptaxids (19 characters, 68 states) known from the three mountains. The Boucardicus cladogram was marginally robust; it supported monophyly of the genus, and it implied evolutionary trends toward larger, more colour-patterned, more globose shells hatched from larger eggs; toward a dorsally and more weakly papillate penis with a large, external gland; and toward a broad-based, tightly convoluted fertilization pouch-seminal receptacle complex with an internal, muscular funnel. A convergence in high-spired shells supported the recent synonymization of Madecataulus under Boucardicus. According to the cladogram, a three-lobed apertural peristome was plesiomorphic, was lost, then reappeared convergently. Among the 12 dissected species of Boucardicus, morphology of the female reproductive system was extremely variable (11 of 14 character states autapomorphic). The Reticulapex cladogram supported monophyly of the genus but gave no robust resolution among species. Recent surveys also indicate that Reticulapex is rare to absent in northern Madagascar. The streptaxid cladogram suggested a sister-group relationship between the endemic clades Paruedentulina and Streptostele (Makmconche), but provided no robust resolution among species within either clade or within Gulella. Anatomical material is relatively scarce for Madagascan streptaxids. Vicariance-biogeographic analysis resulted in the area cladogram (northern Vohimena mountain chain (southern Vohimena chain (southern Anosy chain))). The Vohimena chain, already known for its significantly greater diversity and endemism than the Anosy chain, thus also seems to harbour the older, more plesiomorphic species; this heightens the urgency for conservation and further survey within the Vohimena chain. Acavids (115 species known) remain the most accessible of Madagascar's major, widespread land-snail groups for island-wide phylogenetics and biogeography, mainly because of existing frozen-tissue collections, which have a limited shelf life. Boucardicus (177 species and 6 subspecies known) is clearly the second most accessible.