Systematics, phylogeny and biogeography of the larger camaenid land snails of eastern Queensland rainforests: (Pulmonata: Stylommatophora: Camaenidae)

Scott, Bronwen (1996) Systematics, phylogeny and biogeography of the larger camaenid land snails of eastern Queensland rainforests: (Pulmonata: Stylommatophora: Camaenidae). PhD thesis, James Cook University of North Queensland.

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Abstract

Phylogenetic relationships of Camaenidae, a diverse family of pulmonate land snails with a disjunct distribution in Australasia and Central America, were investigated using a cladistic analysis of the superfamily Helicoidea. The analysis was based on anatomical characters from a previous study by Tiller (1989). Monophyly of the family was examined by splitting Camaenidae into two geographical groups (American and Australasian). Successive weighting generated a single most parsimonious cladogram, which suggested that the Camaenidae is a polyphyletic taxon. Evidence from this analysis demonstrated that the American component of the Camaenidae is closely related to the Helicidae (a European family) and Helminthoglyptidae (a North American family), and the Australasian component is sister group to the Bradybaenidae (principally of eastern and south-eastern Asia).

The phylogenetic relationships and worldwide distribution of Helicoidea were used to examine current palaeogeographical hypotheses using cladistic biogeographic methods. The pattern of vicariance for the Helicoidea indicated that families originated with the break up of eastern Gondwana and Laurasia between the late Mesozoic and mid-Tertiary, and possible vicariance events were identified. It was proposed that Asian terranes, located between India and Australia, maintained contact with northern Australia until the late Cretaceous, which is later than is suggested in current palaeogeographical hypotheses.

Over 400 species of Camaenidae have been recorded from Australia, of which approximately 14% have been described from the rainforests of the north-east. The larger camaenids of eastern Queensland and New South Wales rainforests belong to the hadroid camaenids, a monophyletic group within the subfamily Camaeninae defined by the possession of a well-developed eversible headwart. Histological investigations suggested that the eversible headwart of the hadroid camaenids was homologous to the permanently everted headwart of the Bradybaenidae, sister group to the Australasian Camaenidae. Epithelial cells of the camaenid headwart were columnar and similar in size to those of the surrounding integument, in contrast to the much thicker epithelium of the bradybaenid headwart. Subepithelial glands in the camaenid headwart were less diverse and less abundant than those in the surrounding integument, suggesting that mucous secretion was not an important function of the headwart. Reduction in amount of pigment under the headwart, together with the siting of the headwart over the cerebral ganglion, may indicate a role in determining photoperiod.

The genera and species of hadroid camaenids from eastern Queensland rainforests were revised in this study, using conchological and reproductive tract characters. Genera recognised within this Glade were Hadra Albers, Thersites Pfeiffer, Sphaerospira MOrch, Varohadra Iredale, Zyghelix Iredale, Bentosites Iredale and Temporena Iredale and two new genera from mid-east Queensland. Thirty-one species belonging to these nine genera were recognised, including three new species.

Phylogenetic relationships of the hadroid camaenids were determined by cladistic analysis based on anatomical and conchological characters. The New South Wales genus Meridolum was identified as the most primitive, while the red-bodied snails (Bentosites, Temporena and Gen. nov. A) were determined to be the most advanced. Meridolum and non-hadroid Camaeninae inhabit open woodland, so the evolutionary trend within the hadroids may involve adaptations towards occupation of a more mesic and stable habitat (rainforest).

Reproductive structures which demonstrated the greatest morphological variation within the hadroid camaenids were those of the distal male reproductive tract. These changes were restricted to the epiphallus and penis, both of which are directly involved in copulation. Variation in distal male genitalia was species-specific, but this was not attributable to reproductive character displacement, as there were no differences between the degree of divergence of genitalia in allopatric and sympatric pairs. Female choice might be regarded as the cause of divergence, but evidence in support of this hypothesis is inconclusive.

The biogeography of the hadroid camaenids was examined by cladistic analysis. Distributions of species of hadroid camaenids indicated that eastern Queensland was divided into 41 biogeographical areas, suggesting that continuity in rainforest blocks (e.g. Wet Tropics) is a secondary phenomenon, the result of re-adjustment of rainforest ranges following vicariance events. Cladistic analysis generated biogeographical hypotheses for Cape York Peninsula and the Wet Tropics, north-east and mid-east Queensland, Bowen and the Whitsunday Group, and south-east Queensland. Results supported the conclusions of Joseph, Moritz and Hugall (1993) about relationships between north-east, mid-east and south-east Queensland. The effect of Tertiary and Quaternary climate changes and the role of aridity, marine transgressions and increased rainfall in fragmenting ancestral rainforests were discussed. Rises in sea level and pluvial inundation were regarded, as creating significant barriers for land snails and other taxa.

Principal conclusions of this study are: Camaenidae is a polyphyletic family, which can be separated into American and Australasian components; Bradybaenidae is sister group to the Australasian Camaenidae; Australasian Camaenidae has a Gondwanan origin; South-east Asian terranes rifted from Australia later than current palaeogeographical hypotheses predict; headwart of Australasian Camaenidae is homologous to the bradybaenid headwart; camaenid headwart may not secrete pheromones, but may be important in determining day-length; hadroid camaenids form a coherent group, the . phylogeny of which can be represented by cladistic analysis of conchological and anatomical data; eastern Queensland is composed of at least 41 distinct biogeographical areas; the sequence of vicariance events in eastern Queensland may be determined by cladistic analysis of hadroid camaenid genera; major biogeographic barriers may be the result of marine transgressions or pluvial inundation; species-specific genital morphology is not the result of reproductive character displacement; and multiple mating may result in spermatophore displacement.

Item ID: 33792
Item Type: Thesis (PhD)
Keywords: biogeography; Camaenidae; cladistics; classification; Helicoidea; land snails; phylogeny; Pulmonates; rain forests; rainforests; snails; taxonomy; terrestrial gastropod mollusks
Date Deposited: 21 Jul 2015 05:13
FoR Codes: 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060301 Animal Systematics and Taxonomy @ 50%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060309 Phylogeny and Comparative Analysis @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 100%
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