Distribution and geographic variation of sea kraits in the Laticauda colubrina complex (Serpentes, Elapidae, Laticaudinae)

Heatwole, Harold (2010) Distribution and geographic variation of sea kraits in the Laticauda colubrina complex (Serpentes, Elapidae, Laticaudinae). PhD thesis, James Cook University.

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Abstract

The sea kraits constitute a genus (Laticauda) of marine snakes that forage in the sea but come onto land to rest, digest their prey, court, mate and oviposit. There are three complexes: (1) the Laticauda semifasciatus complex with two species, (2) the Laticauda laticaudata complex with two species, and (3) the Laticauda colubrina complex with four species: Laticauda colubrina, Laticauda frontalis, Laticauda saintgironsi, and Laticauda guineai, the last two of which were described as new to science as a result of the research presented in this dissertation. The Laticauda colubrina complex is far-flung in the tropics and subtropics from the Andaman Islands to Tonga and from New Guinea to the Ryukyu Islands, wherein its species inhabit coral reefs associated with small offshore islands. This area has had an exceptionally complex geologic history involving the collision of the Indian, Eurasian, and Australian tectonic plates, as well as large-scale movements of various marine ophiolites and island arcs and of terranes of various ages and origins (e.g., Gonwanaland and Australia) that became compositely incorporated into the archipelagos now inhabited by sea kraits. The origin, adaptive radiation, and spread of the genus Laticauda took place from 30 mya to the present time, thereby bracketing the time-period relevant to the elaboration of the pattern of geographic variation and speciation of the Laticauda colubrina complex analysed in this dissertation.

This dissertation describes the distributions and patterns of geographic variation of the species in the L. colubrina complex and interprets them in terms of the geologic and palaeogeographic history of the region and of such present-day environmental factors as temperature, directions of sea currents, and distances between areas of suitable habit. The accumulated specimens deposited over several centuries in the museums of the world were used to plot distributions of species and as a source of data on morphological characters and details for use in analysing patterns of geographic variation.

Four approaches to geographic variation in morphology and colour pattern were used: (1) Hierarchical Analysis, (2) Principal Components Analysis and Canonical Discriminant Analysis, (3) construction of phenotypically based trees, and (4) multivariate analysis. The last three are standard techniques, but the first I devised myself. It has the advantage over other morphological techniques of being able to distinguish between populations whose morphologic similarities arise either from (1) convergent evolutionary responses to similar environments or (2) direct effects of similar environments on developmental processes, in contrast to those that (3) reflect genetic relatedness. With the growing recognition that neither morphological nor biochemical techniques alone are sufficient to asses phylogenetic history completely, this technique is an important one in that it bridges the two approaches, and provides a rational basis for selecting target populations for the application of biochemical methods to phylogeographic studies.

The hierarchical approach identified six areas in which populations were relatively homogeneous but which showed discontinuites with adjacent areas. These were: (1) a North-South Axis (Sabah, Philippines, Ryukyus, and Taiwan), (2) an East- West Axis (Andaman and Nicobar Islands, Thailand, Myanmar, Indonesia, Peninsula Malaysia/Singapore, New Guinea excluding southern Papua and West Irian, Solomon Islands), (3) southern Papua , (4) Palau, (5) the Eastern Islands (Vanuatu, Fiji, Tonga), and (6) New Caledonia.

The isolate on New Caledonia was recognized as a new species, Laticauda saintgironsi (published elsewhere; Cogger and Heatwole, 2006) as was the one in southern Papua (Laticauda guineai; also published elsewhere; Heatwole et al., 2005); Laticauda frontalis was elevated from previous synonymy (published elsewhere; Cogger and Heatwole, 2006).

The Principal Components Analysis confirmed these results in a more quantitative way, emphasized the distinctiveness of L. saintgironsi, L. guineai, and L. frontalis and, although confirming the distinctiveness of the other populations demarcated by the hierarchical approach, demonstrated that separation among the two axes and the eastern islands was not as marked as for the named species, thereby supporting the decision not to recognise those differences nomenclaturally. This approach also identified character displacement between L. colubrina and L. frontalis on Vanuatu, the only incidence of sympatry among members of the complex.

The construction of phenetically based trees supported the interpretation that L. frontalis and L. saintgironsi were closely related but did not contribute much otherwise to an understanding of geographic patterns of variation within the complex.

Multivariate analysis revealed that there was a strong latitudinal component to the variation of L. colubrina and that the latitudinal effect varied with longitude. Addition of rainfall and surface temperature of the sea as variates explained little additional variation.

There was sexual dimorphism in many characters, perhaps related to the ecological segregation of males and females into distinct econes with different foraging habits and diets. L. frontalis was less dimorphic than the other species. There was also differences in some characters between juveniles and adults, perhaps reflecting different selective forces operating on juveniles and adults (the two groups are different in the time they spend on land as opposed to in the sea).

A model of the phylogeny and dispersal of sea kraits was developed. It indicates origin of Laticauda in New Guinea from an Asian elapine ancestor. Subsequent radiation involved successive cycles of dispersal during periods of lowered sea levels and isolation during elevated sea levels, giving rise first to the three complexes of the genus, then to the species within complexes, and most recently to the groupings of the east-west axis, north-south axis and eastern islands. These events took place within the past 30 million after most of the formative tectonic and vicariant events of the region had already taken place. Rather, distribution and geographic patterns of variation relate to configuration of land and sea in the area from 30 mya to the present.

Item ID: 19027
Item Type: Thesis (PhD)
Keywords: sea kraits, taxonomy, geographic variations, Elapidae, Laticauda colubrina complex, sea snakes, biogeography, phylogeography, comparative phylogenetics, evolutionary history
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Heatwole, H., Busack, S., and Cogger, H. (2005) Geographic variation in sea kraits of the Laticauda colubrina complex (Serpentes: Elapidae: Hydrophiinae; Laticaudini). Herpetological Monographs 19: 1-136.

Cogger, H., and Heatwole, H. (2006) Laticauda frontalis DeVis and Laticauda saintgironsi sp. nov. representing a new clade of sea kraits from the Republic of Vanuatu and New Caledonia (Serpentes: Laticaudidae). Records of the Australian Museum 58: 245-256.

Date Deposited: 28 Nov 2011 23:07
FoR Codes: 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060301 Animal Systematics and Taxonomy @ 34%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060302 Biogeography and Phylogeography @ 33%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060309 Phylogeny and Comparative Analysis @ 33%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960803 Documentation of Undescribed Flora and Fauna @ 34%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 33%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960802 Coastal and Estuarine Flora, Fauna and Biodiversity @ 33%
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