Vicariance or dispersal? Historical biogeography of three Sunda shelf murine rodents (Maxomys surifer, Leopoldamys sabanus and Maxomys whiteheadi)

Abstract

The Sunda region of south-east Asia comprises the Malay Peninsula and the islands of Java, Sumatra and Borneo, all of which lie on a shallow continental shelf projecting from Indochina. Pleistocene glacial cycles caused sea levels to drop repeatedly, exposing vast areas of the Sunda shelf and creating land bridges among the islands and mainland. These land bridges, the latest of which connected all three of the major Sunda islands to the Malay Peninsula as recently as 9500 years ago, may have enabled mammalian migrations across the Sunda shelf. Pleistocene land bridges on the Sunda shelf have been invoked to explain the current distributions of mammalian taxa occupying ranges corresponding with the Pleistocene limits of land and the appearance of new mammal species in the Pleistocene fossil record. The ability of mammals to move throughout the exposed shelf during periods of low sea level would, however, have been influenced by topographic and ecological features, which have been variously described as savanna-like or as moist tropical rain forest. Using a phylogeographical approach, we test the hypothesis that Pleistocene land bridges enabled widespread movements in three rain-forest-restricted murine rodents of the Sunda shelf: Maxomys surifer, Leopoldamys sabanus and Maxomys whiteheadi. Our results do not support the hypothesis of broad Pleistocene migrations in these taxa, but instead suggest a deep history of vicariant evolution that may correspond with the Pliocene fragmentation of the Sunda block.

Speciation and phylogeography of the Southeast Asian Anopheles sundaicus complex

“…During glacial periods, when sea level was low, the shelf was widely exposed and arid conditions occurred. However, persistent rain-forest refugia were recently hypothesised to have existed in northern Sumatra, northeastern Borneo and peninsular Malaysia (Brandon-Jones, 1996;Gathorne-Hardy et al, 2002;Gorog et al, 2004). During interglacial periods, when sea level was high, the continent and different islands were isolated, experiencing a widespread tropical climate.…”

“…These cyclical bottlenecks could have also erased or modified ancestral polymorphism. Such lack of information might explain the inability to resolve basal relationships among clades, as well as the incongruence between Cyt-b and COI markers indicated by the ILD test (Andreev et al, 1998;Gandolfi et al, 2001;Gorog et al, 2004). Seng et al (2001) suggested that the different ecological patterns of A. sundaicus s.l.…”

Speciation dynamics in the SE Asian tropics: Putting a time perspective on the phylogeny and biogeography of Sundaland tree squirrels, Sundasciurus

“…When repeated several times throughout the Pleistocene, this system has the potential to generate a lot of diversity. This hypothesis has been supported by low levels of genetic divergence between populations of some Sunda shelf mammals (Campbell et al, 2004(Campbell et al, , 2006Gorog et al, 2004;Lucchini et al, 2005;Roos et al, 2003). However, the vegetation during the Pleistocene glacial periods was undoubtedly very different from the present, and the interactions between climate and sea level and their effects on the distribution of the fauna and flora is complex (van den Bergh et al, 2001).…”

“…Under this scenario, populations diverge and speciate in allopatry when sea level is high, and then expand their range when sea levels are low and the islands are connected by land (Gorog et al, 2004; see also Steppan et al, 2003). When repeated several times throughout the Pleistocene, this system has the potential to generate a lot of diversity.…”

“…For example, Cranbrook (2000) interpreted the large mammal fauna of the Pleistocene of coastal Borneo as being more adapted to savannas than to the rainforests of the present. Gorog et al (2004) adduced evidence that populations of rainforest rats on the Sunda Islands and Malay Peninsula (Maxomys and Leopoldamys) became isolated from one another in the mid-to late Pliocene, perhaps 2 million years ago. This evidence may support the museum or stasis hypothesis, which states that the high diversity in the tropics was generated over a much longer time period due to high ecological stability (Gathorne-Hardy et al, 2002;Morley, 2002).…”