Molecular phylogeny of an endemic radiation of Cuban toads (Bufonidae: Peltophryne) based on mitochondrial and nuclear genes

Aim In this study we present a molecular phylogenetic and phylogeographical analysis of Peltophryne (Anura: Bufonidae), an endemic genus of Antillean toads, to investigate the spatial and temporal origins of the genus, with particular focus on the eight Cuban species. Location Greater Antilles, with extensive sampling of the Cuban archipelago. Methods We obtained DNA sequence data from two mitochondrial genes, cytochrome c oxidase subunit I (COI) and ribosomal RNA (16S), for 124 toads representing all eight Cuban species, and combined this with published data from Hispaniola (one of three species) and Puerto Rico (one of one species) to establish a molecular phylogeny for Peltophryne. In addition, we explored the phylogeographical structure of widespread Cuban species. For a subset of 42 toads we also obtained DNA sequence data from two nuclear genes, recombination activator‐1 (RAG‐1) and chemokine receptor 4 (CXCR‐4). We combined our molecular data with published DNA sequences from a global sample of bufonid toads to place the spatial and temporal origins of Peltophryne in the Caribbean within a fuller geographical and phylogenetic context. Results All phylogenetic analyses supported the monophyly of West Indian toads. The ancestor of Peltophyrne diverged from its mainland source around the Eocene–Oligocene boundary, with a subsequent radiation across the Caribbean islands taking place during the Miocene. Cuban species are monophyletic with a basal split in the early–middle Miocene that separates extant small‐bodied from large‐bodied species. Extensive mitochondrial DNA (mtDNA) sampling within widespread Cuban species revealed contrasting phylogeographical patterns. Peltophryne taladai and P. empusa showed deeply divergent lineages, whereas no geographical structure was observed in the widespread P. peltocephala. Main conclusions Our timeline for Peltophryne diversification is consistent with a biogeographical model requiring no long‐distance overwater dispersal. Although confidence intervals on divergence time estimates are wide, the stem age of Peltophyrne coincides with the hypothesized GAARlandia landspan or archipelago, which may have connected South America briefly with the Antilles. The ages of Peltophryne for Puerto Rico, Hispaniola and Cuba are consistent with a recently proposed vicariance scenario for the region. Our molecular results support the recognition of all eight species in Cuba, and provide evidence of possible cryptic species.     

Morphological and isozyme divergence in Korean Hepatica sensu stricto (Ranunculaceae)

 Morphological and electrophoretic data were studied to examine species delimitation, patterns of morphological and genetic variation in three Korean Hepatica including two endemics, H.␣maxima and H. insularis. Based on a phenogram using 15 morphological characters, taxa were distinct; it was consistent with the phenogram based on genetic distance. In the enzyme electrophoresis study, the genetic identities suggested that three taxa were genetically divergent enough to be recognized as different species, falling within the range expected␣for congeners. The genetic identity between H.␣asiatica and H. insularis was higher than the values between these two taxa and H.␣maxima, a restricted endemic of Ulleung Island. The least genetic variation was found in H. maxima and the greatest in widespread H. asiatica. These data are consistent with theoretical expectations that small populations are more likely to be genetically depauperate. Received November 13, 2001; accepted May 10, 2002 Published online: December 11, 2002     

Divergence maintained by climatic selection despite recurrent gene flow: a case study of Castanopsis carlesii (Fagaceae)

Local adaptation to different environments has the potential to maintain divergence between populations despite recurrent gene flow and is an important driver for generating biological diversity. In this study, we investigate the role of adaptation in the maintenance of two parapatric varieties of a forest tree. We used sequence variation of chloroplastic DNA and restriction site‐associated DNA to investigate the genetic structure of two varieties of Castanopsis carlesii in subtropical China and relate it to climatic variation. We used niche reconstruction methods to investigate niche differentiation between the two varieties and to estimate the past distribution of this species. A deep divergence was observed between the two varieties, but evidence of introgression and genetic admixture was detected in two phenotypically and geographically intermediate populations. Niche reconstruction suggests that the distribution of the two varieties was disjunct during periods of global cooling and that the two varieties occupy significantly different niches. The genetic structure was mainly driven by environmental factors, and 13 outlier loci under divergent selection were correlated with climatic variation. These results suggest that the two varieties evolved in allopatry and came back into secondary contact after the last glacial maximum and that they are an evolutionary example of divergence maintained by climatic selection despite recurrent gene flow.     

Phylogeography of the fiscal shrike (Lanius collaris): a novel pattern of genetic structure across the arid zones and savannas of Africa

Aim Savanna occupies a substantial part of Africa, being distributed around the two major tropical rain forest blocks in what is referred to as the Savanna Belt. Our current understanding of the genetic structure within species distributed across the Savanna Belt is primarily derived from mammalian taxa, studies of which have revealed a suture zone or transition between northern and east/southern Africa clades in south‐western Kenya and north‐western Tanzania. We conduct a phylogeographic study of the fiscal shrike (Lanius collaris), a polytypic species distributed across the Savanna Belt of Africa and for which morphological and vocal data are in agreement with the suture zone recovered for mammalian taxa, to test the hypothesis of a spatially congruent genetic break across several taxa, including birds. Location Africa, south of the Sahara. Methods We analysed DNA sequences recovered from four loci (one mitochondrial, two autosomal and one Z‐linked) in 66 individuals, representing all recognized subspecies, as well as putatively closely related species. We make use of a combination of tree‐building and population genetic methods to investigate the phylogeographic structure of the fiscal shrike across Africa. Results The fiscal shrike consists of two primary lineages with a strong geographic component: a northern group distributed from southern Tanzania to Senegal, and a southern group distributed from Botswana/Zambia to South Africa with isolated populations in Tanzania and northern Malawi. Unexpectedly, Souza’s shrike (L. souzae) was nested within L. collaris, as the sister group of the southern group. The positions of Mackinnon’s shrike (L. mackinnoni) and that of the São Tomé shrike (L. newtoni) were variable, being either nested within the fiscal shrike or sister to the L. collaris–L. souzae clade. Our divergence time analyses suggest that the Lanius collaris species complex started to diversify around 2.2 Ma. Main conclusions Our study reveals a distinct biogeographic pattern for a savanna distributed species in Africa, with the transition between the two primary genetic lineages occurring at a latitude of c. 15–16° S, 10° S further south than shown elsewhere for several mammalian species.     

Ecotypic divergence in Crepis tectorum (Asteraceae): inferring trait lability and correlational constraints from hormonally manipulated phenotypes

Despite long‐standing interest in the evolutionary role of plant hormones, relatively few studies have used hormonally manipulated phenotypes to address questions about phenotypic evolution in plants. In the present investigation, I subjected plants of Crepis tectorum subsp. pumila to simple gibberellin (GA) treatments under both field and greenhouse conditions to assess developmental lability and correlational constraints of phenotypic traits that distinguish this dwarf ecotype from conspecific populations of the much taller weed ecotype (subsp. tectorum). The hormonally manipulated plants largely phenocopied the weed ecotype in leaf shape, plant stature and branching habit, indicative of both high lability and tight integration of traits reflecting gross morphology. Floral size traits sometimes declined after GA application, especially under field conditions. The latter result conflicts with the positive correlations between floral and vegetative size traits seen in previous comparative analyses and point to a tradeoff that could act as a constraint on ecotype divergence. The response to GA was consistent in direction for most traits, as opposed to the magnitude of response, which varied depending on the trait, the population, the growing environment and the timing and level of hormone application. Taken together, the results highlight the potential for simple hormonal changes to cause large, plastic shifts in phenotype, but also illustrate the constrained nature of such influences.