No abstract

Madagascar is one of the world's hottest biodiversity hot spots due to its diverse, endemic, and highly threatened biota. This biota shows a distinct signature of evolution in isolation, both in the high levels of diversity within lineages and in the imbalance of lineages that are represented. For example, chameleon diversity is the highest of any place on Earth, yet there are no salamanders. These biotic enigmas have inspired centuries of speculation relating to the mechanisms by which Madagascar's biota came to reside there. The two most probable causal factors are Gondwanan vicariance and/or Cenozoic dispersal. By reviewing a comprehensive sample of phylogenetic studies of Malagasy biota, we find that the predominant pattern is one of sister group relationships to African taxa. For those studies that include divergence time analysis, we find an overwhelming indication of Cenozoic origins for most Malagasy clades. We conclude that most of the present-day biota of Madagascar is comprised of the descendents of Cenozoic dispersers, predominantly with African origins. Ignoring temporal information obscures the connection between biogeographic patterns and their underlying causes. Donoghue & Moore, 2003 You're either on the bus, or off the bus.

Serine residues 338 and 339 in the carboxyl-terminal tail of the type II go-nadotropin-releasing hormone receptor are critical for-arrestin-independent inter-nalization. Endocrinology 2004; 145: 4480-4488. 62 Springer MS, Murphy WJ, Eizirik E, O'Brien SJ: Placental mammal diversification and the Cretaceous-Tertiary boundary.

The lemurs of Madagascar are a unique radiation of primates that show an extraordinary diversity of lifestyles, morphologies and behaviours. However, very little is known about the relative antiquity of lemuriform clades due to the lack of terrestrial fossils for the Tertiary of Madagascar. Here, we employ a Bayesian method to estimate divergence dates within the lemuriform radiation using several unlinked gene loci and multiple fossil calibrations outside the lemuriform clade. Two mitochondrial genes (cytochrome oxidase II and cytochrome b), two nuclear introns (transthyretin intron 1 and von Willebrand factor gene intron 11) and one nuclear exon (interphotoreceptor retinoid binding protein, exon 1) are used in separate and combined analyses. The genes differ in taxon sampling and evolutionary characteristics but produce congruent date estimates. Credibility intervals narrow considerably in combined analyses relative to separate analyses due to the increased amount of data. We also test the relative effects of multiple vs. single calibration points, finding that, when only single calibration points are employed, divergence dates are systematically underestimated. For the mitochondrial DNA data set, we investigate the effects of sampling density within the mouse lemur radiation (genus Microcebus). When only two representative species are included, estimated dates throughout the phylogeny are more recent than with the complete-species sample, with basal nodes less affected than recent nodes. The difference appears to be due to the manner in which priors on node ages are constructed in the two analyses. In nearly all analyses, the age of the lemuriform clade is estimated to be approximately 62-65 Ma, with initial radiation of mouse lemurs and true lemurs (genus Eulemur) occurring approximately 8-12 Ma. The antiquity of the mouse lemur radiation is surprising given the near uniform morphology among species. Moreover, the observation that mouse lemurs and true lemurs are of similar ages suggests discrepancies in rates of morphological, behavioural and physiological evolution in the two clades, particularly with regard to characteristics of sexual signalling. These differences appear to correlate with the nocturnal vs. diurnal lifestyles, respectively, of these two primate groups.

We report new evidence that bears decisively on a long-standing controversy in primate systematics. DNA sequence data for the complete cytochrome b gene, combined with an expanded morphological data set, confirm the results of a previous study and again indicate that all extant Malagasy lemurs originated from a single common ancestor. These results, as well as those from other genetic studies, call for a revision of primate classifications in which the dwarf and mouse lemurs are placed within the Afro-Asian lorisiforms. The phylogenetic results, in agreement with paleocontinental data, indicate an African origin for the common ancestor of lemurs and lorises (the Strepsirrhini). The molecular data further suggest the surprising conclusion that lemurs began evolving independently by the early Eocene at the latest. This indicates that the Malagasy primate lineage is more ancient than generally thought and places the split between the two strepsirrhine lineages well before the appearance of known Eocene fossil primates. We conclude that primate origins were marked by rapid speciation and diversification sometime before the late Paleocene.Although strepsirrhine (we use the term strepsirrhine to define the living tooth-combed primates, their immediate ancestor, and all of its descendants) primates comprise more than one-third of the living members of the primate order, there is no current consensus concerning their phylogeny, classification, or time of divergence. Phylogenetic debate centers around two groups of Malagasy lemurs, the mouse and dwarf lemur group (family Cheirogaleidae) and the aye-aye (family Daubentoniidae). Morphologists inferred from the basicranial anatomy of the cheirogaleids that these animals are actually members of the Afro-Asian loris group (1, 2). This hypothesis was widely accepted and reflected in the majority of modern primate classifications (3-6). Cladistic studies of DNA sequences (7-9) have failed to support the lorisiform association, however, and have found instead that cheirogaleids belong within a Malagasy primate clade, thereby agreeing with an early synthetic view (10) and with genetic distance studies (11-13). The unusual morphological specializations of the aye-aye (e.g., ever-growing rodent-like incisors, clawed digits, and an extremely elongated middle finger) have made it difficult to place within strepsirrhine phylogeny also. One morphology-based hypothesis claims that the aye-aye comprises a monotypic sister group to all remaining strepsirrhines (14, 15); another holds that the phylogenetic position of the aye-aye is indeterminate relative to all other primates (16). DNA sequence studies have likewise given conflicting results. A study of mitochondrial DNA placed the aye-aye at the base of the strepsirrhine clade (7), whereas a study of nuclear DNA placed it securely with the other Malagasy primates (9).The resolution of these controversies is important for our understanding of both primate phylogeny and historical bio- Another area of debate concerns strepsirrhine ...