A multidimensional approach for detecting species patterns in Malagasy vertebrates

Abstract

The biodiversity of Madagascar is extraordinarily distinctive, diverse, and endangered. It is therefore urgent that steps be taken to document, describe, interpret, and protect this exceptional biota. As a collaborative group of field and laboratory biologists, we employ a suite of methodological and analytical tools to investigate the vertebrate portion of Madagascar's fauna. Given that species are the fundamental unit of evolution, where micro- and macroevolutionary forces converge to generate biological diversity, a thorough understanding of species distribution and abundance is critical for understanding the evolutionary, ecological, and biogeographic forces that have shaped Malagasy vertebrate diversity. We illustrate the means by which we apply Mayr's "three basic tasks" of the systematist [Mayr, E. (1942) Systematics and the Origin of Species from the Viewpoint of a Zoologist (Harvard Univ. Press, Cambridge, MA)] to identify, classify, and study the organisms that together constitute Madagascar's vertebrate community. Using field inventory methods, specimen-based studies, and morphological and molecular analyses, we formulate hypotheses of species identity that then serve as the foundation for subsequent studies of biology and history. Our experience, as well as that of other investigators, has shown that much of the vertebrate species diversity in Madagascar is "cryptic" for both biological and practical reasons. Beyond issues of cryptic biological diversity, the resolution of species identity in Madagascar has been hampered because of a lack of vouchered comparative material at the population level. Through our activities, we are attempting to remedy these limitations while simultaneously enhancing research capacity in Madagascar.

Fig. 1.

Molecular phylogeny of plated lizards. Shown is a parsimony tree based on full-length cytochrome b sequences. Numbers indicate bootstrap support and posterior probability scores for clades representing various species. Sampling localities are as follows: Northern Madagascar (N) 1, Ankarana; N2, Analamera; N3, Ambre; N4, Daraina. Northeastern Madagascar (NE) 1, Anjanaharibe-Sud; NE2, Antalaha; NE3, Betaolana; NE4, Marojejy; NE5, Tampolo. Northwestern Madagascar (NW) 1, Lokobe; NW2, Manongarivo; NW3, Ambanja; NW4, Ankarafantsika. Eastern Madagascar (E), Mantadia. Central Madagascar (C), Andranomay. South central Madagascar (SC) 1, Itremo; SC2, Vinanintelo; SC3, Manambolo; SC4 Vohipaha; SC5, Ivohibe; Western Madagascar (W) 1, Ambatomainty; W2, Bemaraha; W3, Ambohijanahary. Southeastern Madagascar (SE) 1, Petriky; SE2, Andohahela; SE3, Midongy-Sud. Southwestern Madagascar (SW) 1, Kirindy Mitea; SW2, Mike-Abrahama/Andalandomo/Ankotapike; SW3, Andotabo; SW4, Tsimanampetsotsa; SW5, Analavelona. Habitat abbreviations are: DF (dry forest); ERF (evergreen rainforest); WLS (woodland savannah); S (scrub and heath land), TF (transitional forest); SD (semideciduous forest); D (deciduous forest); GL (grass land); Er (ericoid forest). Sequences are deposited in the GenBank database under accession nos. DQ004403-DQ004461. (Adapted from A.P.R., K.P.K., and A.D.Y., unpublished work.)

Fig. 2.

Comparison of phylogenetic and biogeographic structure in Malagasy trident bats (genus Triaenops). (A) T. auritus (resurrected from synonom) (J.R. and S.M.G., unpublished work) and T. furculus show very distinct segregation into northern and southern distributions (indicated by solid line). (B) T. rufus shows diffuse distribution with no apparent biogeographic structure. (C) Comprehensive Triaenops phylogeny reveals that Malagasy taxa are paraphyletic with respect to African species, T. persicus. Sequences are deposited in the GenBank database under accession nos. DQ005718-DQ005850. (Adapted from A.L.R., E. Palkovacs, J.R., S.M.G., and A.D.Y., unpublished work.)

Fig. 3.

Overview of the approach used to clarify species limits in long-tailed shrew tenrecs and the subsequent insights into geographic variation and community structure. (a) Phylogeographic analysis of mtDNA recovers two cryptic, highly divergent, yet broadly sympatric (and in many cases syntopic), haplotype clades (clades A and B) within the single nominal species of long-tailed shrew tenrec, M. longicaudata. (b) Despite their striking morphological similarity, members of each haplotype clade are readily distinguished by both a priori and a posteriori morphometric analyses, supporting the recognition of two cryptic species, M. longicaudata (clade A, round symbols) and M. majori (clade B, square symbols). (c) The revised species-level taxonomy provides insights into biogeography and geographic variation. For example, contrasting patterns of clinal variation in body size were previously obscured. (d) Reevaluation of a published study of tenrec community assembly in fragmented forest patches (79) in light of the revised taxonomy shows that both species coexist in remarkably small habitat patches. Sequences are deposited in the GenBank database under accession nos. AY193297-AY193416. (Adapted from figures and text in ref. .)

Fig. 4.

Graph of the number of publications focusing on genus Microcebus from 1970 through 2003. Increased publication activity seems to correlate with increased number of recognized species. Publication numbers were determined by means of a survey of ISI Web of Science.

Fig. 5.

Fig. 5 illustrates the lack of precise correlation between morphometric distinctiveness and genetic divergence in mouse lemur species. The results of discriminant function analysis of 34 cranial, dental, and external morphometric characters are redrawn from ref. . Functions 1 and 2 (A) show conspicuous discrimination of Microcebus berthae from other species, but otherwise do not discriminate well among species. Functions 2 and 3 (B) show discrimination of all species, with Microcebus berthae remaining as highly distinct. (C) A maximum likelihood phylogram of species-specific haplotypes derived from the fibrinogen α intron 4 locus illustrates that Microcebus berthae and Microcebus myoxinus are genetically very similar. Conversely, Microcebus ravelobensis is genetically and phylogenetically divergent.

Fig. 6.

Minimum spanning network of the fibrinogen α intron 4 (609 bp) in genus Microcebus. This network was calculated in arlequin 2.000 (80) using pairwise differences between haplotypes. Each shading represents an individual species. Numbers inside circles and squares are the number of individuals sharing a haplotype; empty circles equal one individual. Numbers on connecting lines are the number of nucleotide changes separating each haplotype; empty lines equal one change. Note that all alleles for Microcebus ravelobensis are species-specific and are highly diverged from alleles sampled from other species. Conversely, the allele in greatest frequency within the myoxinus-berthae-rufus1 clade is identical among the three species. Sequences are deposited in the GenBank database under accession nos. DQ003345-DQ003479. (Adapted from K.L.H., R.R., S.M.G., and A.D.Y., unpublished work.)