An official website of the United States government
ABSTRACT Coalescent modelling of hybrid zones can provide novel insights into the historical demography of populations, including divergence times, population sizes, introgression proportions, migration rates and the timing of hybrid zone formation. We used coalescent analysis to determine whether the hybrid zone between phylogeographic lineages of the Plateau Fence Lizard (Sceloporus tristichus) in Arizona formed recently due to human‐induced landscape changes, or if it originated during Pleistocene climatic shifts. Given the presence of mitochondrial DNA from another species in the hybrid zone (Southwestern Fence Lizard,S. cowlesi), we tested for the presence ofS. cowlesinuclear DNA in the hybrid zone as well as reassessed the species boundary betweenS. tristichusandS. cowlesi. No evidence ofS. cowlesinuclear DNA is found in the hybrid zone, and the paraphyly of both species raises concerns about their taxonomic validity. Introgression analysis placed the divergence time between the parental hybrid zone populations at approximately 140 kya and their secondary contact and hybridization at approximately 11 kya at the end of the Pleistocene. Introgression proportions estimated for hybrid populations are correlated with their geographic distance from parental populations. The multispecies coalescent with migration provided significant support for unidirectional migration moving from south to north, which is consistent with spatial cline analyses that suggest a slow but steady northward shift of the centre of the hybrid zone over the last two decades. When analysing hybrid populations sampled along a linear transect, coalescent methods can provide novel insights into hybrid zone dynamics.
more »
« less
Contrasting Phylogeographic Patterns of Sandy vs. Rocky Sympatric Sister Species of Supralittoral Tylos Isopods in Chile
ABSTRACT Sister taxa that have diverged and persisted in sympatry have likely been exposed to the same general environmental changes throughout their evolutionary history and may thus exhibit similar phylogeographies. Here, we compare the phylogeographic patterns of two sister species of isopods (genusTylos) that have broadly overlapping distributions but distinct habitat preferences in the supralittoral zone of Chile. The dynamic geoclimatic history of this region during the Quaternary has been implicated in shaping the evolutionary histories of other coastal taxa.Tylos spinulosusis found in sandy beaches at latitudes ~27°–30° S, whereasTylos chilensishas been found in rocky shores at ~27°–33° S and at ~39°–42° S. We sampled both species across their ranges (collectively from 20 localities) and obtained sequences from at least one mitochondrial gene for 95 T. chilensisand 41 T. spinulosus. We used phylogenetics and population genetics methods to analyze four single‐gene and one concatenated datasets: 12S rDNA (n = 130); 16S rDNA (n = 31); Cytochrome oxidase subunit I (n = 28); Cytochrome b (n = 24); concatenation of the four genes (n = 24). Both species show high levels of isolation of local populations, consistent with expectations from their limited autonomous dispersal potential. However, they exhibit strikingly different mitochondrial phylogeographic patterns.Tylos chilensisshows evidence of multiple relatively deep divergence events leading to geographically restricted lineages that appear to have persisted over multiple glaciations. Surprisingly, one lineage ofT. chilensiswas found in geographically distant localities, suggesting the possibility of human‐mediated dispersal.Tylos spinulosusappears to have undergone a relatively recent bottleneck followed by a population/range expansion. Differences in life histories and habitat preferences or stochasticity may have contributed to these striking phylogeographic differences. Finally, the high levels of differentiation and isolation among populations indicate that they are highly vulnerable to extirpation. We discuss threats to their persistence and recommendations for their conservation.
more »
« less
- Award ID(s):
- 0743782
- PAR ID:
- 10621158
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology and Evolution
- Volume:
- 15
- Issue:
- 7
- ISSN:
- 2045-7758
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The conversion of natural habitats to human land uses often increases local temperatures, creating novel thermal environments for species. The variable responses of ectotherms to habitat conversion, where some species decline while others persist, can partly be explained by variation among species in their thermal niches. However, few studies have examined thermal niche variation within species and across forest‐land use ecotones, information that could provide clues about the capacity of species to adapt to changing temperatures. Here, we quantify individual‐level variation in thermal traits of the tropical poison frog,Oophaga pumilio, in thermally contrasting habitats. Specifically, we examined local environmental temperatures, field body temperatures (Tb), preferred body temperatures (Tpref), critical thermal maxima (CTmax), and thermal safety margins (TSM) of individuals from warm, converted habitats and cool forests. We found that frogs from converted habitats exhibited greater meanTbandTprefthan those from forests. In contrast,CTmaxandTSMdid not differ significantly between habitats. However,CTmaxdid increase moderately with increasingTb, suggesting that changes inCTmaxmay be driven by microscale temperature exposure within habitats rather than by mean habitat conditions. AlthoughO. pumilioexhibited moderate divergence inTpref,CTmaxappears to be less labile between habitats, possibly due to the ability of frogs in converted habitats to maintain theirTbbelow air temperatures that reach or exceedCTmax. Selective pressures on thermal tolerances may increase, however, with the loss of buffering microhabitats and increased frequency of extreme temperatures expected under future habitat degradation and climate warming. Abstract in Spanish is available with online material.more » « less
-
ABSTRACT AimThe aim of the current study is to conduct a comprehensive phylogenetic analysis of the genusArbaciato elucidate the evolution and phylogenetic relationships among all extant species and reevaluate the presence of geographic structure within species that have wide, fragmented distributions. LocationSpecimens ofArbaciawere collected from 34 localities spanning the Atlantic and Pacific Oceans, and the Mediterranean Sea. MethodsWe obtained sequences from three mitochondrial markers (COI, 16S and the control region and adjacent tRNAs) and two nuclear markers (28S and 18S; the latter ultimately excluded from the final analyses). Phylogenetic trees were constructed using maximum likelihood and Bayesian inference approaches. A time‐calibrated phylogenetic tree was inferred using a relaxed Bayesian molecular clock and three fossil calibration points. ResultsOur analysis supports the monophyly of the genusArbacia, including the speciesArbacia nigra(previously assigned to the monotypic genusTetrapygus). The new phylogenetic topology suggests an alternative biogeographic scenario of initial divergence between Atlantic and Pacific subclades occurring approximately 9 million years ago. The dispersal and subsequent diversification of the Pacific subclade to the southeast Pacific coincides with the onset of glacial and interglacial cycles in Patagonia. In the Atlantic subclade, the split betweenA. punctulataandA. lixulaoccurred 3.01–6.30 (median 3.74 million years ago), possibly associated with the strengthening of the Gulf Stream current connecting the western and eastern Atlantic. Our study also reveals significant genetic and phylogeographic structures within both Atlantic species, indicating ongoing differentiation processes between populations. Main ConclusionOur study provides valuable insights into the evolutionary history and biogeography of the genusArbaciaand highlights the complex interplay between historical climate changes and oceanic currents in shaping the distribution and diversification of echinoids in the Atlantic and Pacific Oceans.more » « less
-
Abstract Introduced plants provide a unique opportunity to examine how plants respond through plasticity and adaptation to changing climates. We compared plants ofSpartina alterniflorafrom the native (United States, 27–43°N) and introduced (China, 19–40°N) ranges. In the field and greenhouse, aboveground productivity of Chinese plants was greater than that of North American plants. Aboveground biomass in the field declined with increasing latitude in the native range, a pattern that persisted in the greenhouse, indicating a genetic basis. Aboveground biomass in the field displayed hump‐shaped relationships with latitude in China, but this pattern disappeared in field and greenhouse common gardens, indicating phenotypic plasticity. Relationships in both geographic regions were explained by temperature, which is probably the underlying environmental factor affecting aboveground biomass.S. alterniflorahas evolved greater biomass in China, but in the four decades since it was introduced, it has not yet evolved the genetic cline in biomass seen in its native range. By working at lower latitudes in the introduced range than have been sampled in the native range, we identified an optimum temperature in the introduced range above which aboveground productivity decreases.more » « less
-
RationaleIt is imperative to understand how chemical preservation alters tissue isotopic compositions before using historical samples in ecological studies. Specifically, although compound‐specific isotope analysis of amino acids (CSIA‐AA) is becoming a widely used tool, there is little information on how preservation techniques affect amino acidδ15N values. MethodsWe evaluated the effects of chemical preservatives on bulk tissueδ13C andδ15N and amino acidδ15N values, measured by gas chromatography/isotope ratio mass spectrometry (GC/IRMS), of (a) tuna (Thunnus albacares) and squid (Dosidicus gigas) muscle tissues that were fixed in formaldehyde and stored in ethanol for 2 years and (b) two copepod species,Calanus pacificusandEucalanus californicus, which were preserved in formaldehyde for 24–25 years. ResultsTissues in formaldehyde‐ethanol had higher bulkδ15N values (+1.4,D. gigas; +1.6‰,T. albacares), higherδ13C values forD. gigas(+0.5‰), and lowerδ13C values forT. albacares(−0.8‰) than frozen samples. The bulkδ15N values from copepods were not different those from frozen samples, although theδ13C values from both species were lower (−1.0‰ forE. californicusand −2.2‰ forC. pacificus) than those from frozen samples. The mean amino acidδ15N values from chemically preserved tissues were largely within 1‰ of those of frozen tissues, but the phenylalanineδ15N values were altered to a larger extent (range: 0.5–4.5‰). ConclusionsThe effects of preservation on bulkδ13C values were variable, where the direction and magnitude of change varied among taxa. The changes in bulkδ15N values associated with chemical preservation were mostly minimal, suggesting that storage in formaldehyde or ethanol will not affect the interpretation ofδ15N values used in ecological studies. The preservation effects on amino acidδ15N values were also mostly minimal, mirroring bulkδ15N trends, which is promising for future CSIA‐AA studies of archived specimens. However, there were substantial differences in phenylalanine and valineδ15N values, which we speculate resulted from interference in the chromatographic resolution of unknown compounds rather than alteration of tissue isotopic composition due to chemical preservation.more » « less
