Sister Species Pairs Research Articles

Allometric scaling in centrarchid fish: origins of intra- and inter-specific variation in oxidative and glycolytic enzyme levels in muscle

The influence of body size on metabolic rate, muscle enzyme activities and the underlying patterns of mRNA for these enzymes were explored in an effort to explain the genetic basis of allometric variation in metabolic enzymes. We studied two pairs of sister species of centrarchid fish: black bass (largemouth bass Micropterus salmoides and smallmouth bass Micropterus dolomieui) and sunfish (pumpkinseed Lepomis gibbosus and bluegill Lepomis macrochirus). Our goal was to assess the regulatory basis of both intraspecific and interspecific variation relative to body size, as well as to gain insights into the evolutionary constraints within lineages. Whole animal routine metabolic rate showed scaling coefficients not significantly different from 1, ranging from (+0.87 to +0.96). However, there were significant effects of body size on the specific activities of oxidative and glycolytic enzymes. Mass-specific activity of the oxidative enzyme citrate synthase (CS) scaled negatively with body size in each species, with scaling coefficients ranging from -0.15 to -0.19, whereas the glycolytic enzyme pyruvate kinase (PK) showed positive scaling, with scaling coefficients ranging from +0.08 to +0.23. The ratio of mass-specific enzyme activity in PK to CS increased with body size, whereas the ratio of mRNA transcripts of PK to CS was unaffected, suggesting the enzyme relationships were not due simply to transcriptional regulation of both genes. The mass-dependent differences in PK activities were best explained by transcriptional regulation of the muscle PK gene; PK mRNA was a good predictor of PK specific enzyme activity within species and between species. Conversely, CS mRNA did not correlate with CS specific enzyme activities, suggesting post-transcriptional mechanisms may explain the observed inter-specific and intraspecific differences in oxidative enzymes.

Comparative phylogeography and speciation of dung beetles from the Australian Wet Tropics rainforest

In tropical rainforests, insects show especially high species richness and local endemism of species relative to vertebrates. One possible cause is that insects respond to historical fluctuations of rainforests on a smaller spatial scale than do vertebrates. To evaluate this hypothesis, we combine environmental niche models and mitochondrial DNA phylogeography for two pairs of sister species of the dung beetle genus Temnoplectron (T. aeneopiceum-T. subvolitans and T. politulum-T. reyi) from the rainforests of northeastern Australia, where climate-driven rainforest fluctuations in the Quaternary have strongly influenced genetic and species diversity of vertebrates. Within both species pairs, the bioclimatic niche was conserved, but the T. aeneopiceum-T. subvolitans species pair had the narrower environmental range, and thus more restricted potential distribution. Coalescent analyses indicated Late Pliocene or Early Pleistocene divergences for both species pairs, and earlier speciation in (T. aeneopiceum-T. subvolitans) than in (T. politulum-T. reyi). Phylogeographic structure in (T. aeneopiceum-T. subvolitans) was more pronounced than in (T. politulum-T. reyi), with significant isolation-by-distance in the former species-pair only. Nested clade and coalescence analyses indicated local range expansions for the T. aeneopiceum-subvolitans species pair and range-wide expansion for both T. politulum and T. reyi. We suggest that stronger phylogeographic structure and earlier divergence in (T. aeneopiceum-T. subvolitans) than in (T. politulum-T. reyi) reflects a stronger influence of environmental barriers to gene flow under the present climate and greater sensitivity to warmer and drier periods of the Quaternary. The two species pairs evidently responded to Quaternary rainforest fluctuations at spatial scales similar to those seen within low-vagility species of vertebrate. Despite this similarity of scale, these insect lineages are reproductively isolated at parapatric boundaries, whereas analogous lineages of vertebrates often are not. We suggest that rapid evolution of genitalia may facilitate geographic speciation in rainforest beetles.

Climatic zonation drives latitudinal variation in speciation mechanisms

Many groups of organisms show greater species richness in the tropics than in the temperate zone, particularly in tropical montane regions. Forty years ago, Janzen suggested that more limited temperature seasonality in the tropics leads to greater climatic zonation and more climatic barriers to organismal dispersal along elevational gradients in the tropics relative to temperate regions. These factors could lead to differences in how species arise in tropical versus temperate regions and possibly contribute to greater tropical diversity. However, no studies have compared the relationships among climate, elevational distribution and speciation in a group inhabiting both tropical and temperate regions. Here, we compare elevational and climatic divergence among 30 sister-species pairs (14 tropical, 16 temperate) within a single family of salamanders (Plethodontidae) that reaches its greatest species richness in montane Mesoamerica. In support of Janzen's hypothesis, we find that sister species are more elevationally and climatically divergent in the tropics than in the temperate zone. This pattern seemingly reflects regional variation in the role of climate in speciation, with niche conservatism predominating in the temperate zone and niche divergence in the tropics. Our study demonstrates how latitudinal differences in elevational climatic zonation may increase opportunities for geographical isolation, speciation and the associated build-up of species diversity in the tropics relative to the temperate zone.

Stress-Induced Color-Pattern Modifications and Evolution of the Painted Lady Butterflies Vanessa cardui and Vanessa kershawi

It has been proposed that phenotypic plasticity and genetic assimilation through natural selection partly determine the direction of divergent selection that eventually results in speciation. To elucidate a process of butterfly color-pattern evolution and speciation in the light of this hypothesis, morphological and physiological differences between a pair of sister species, the Painted Lady butterfly Vanessa cardui and the Australian Painted Lady butterfly Vanessa kershawi, were investigated. Ten different traits of wing color-pattern were indicated, most of which concerned the darker coloration of V. kershawi, with the notable exception of the blue foci at the center of the black focal elements only in V. kershawi. Differences in behavior and life history between the two species appeared to be minimal, but importantly, V. kershawi tends to prefer a "stressful" arid environment. The experimental treatment of pupae of V. cardui either by low temperature or by injection of thapsigargin, a stress-inducing chemical, readily produced individuals with the darker coloration and the blue foci as a result of a general stress response. These stress-induced color-pattern modifications were considered to be the revelation of phenotypic plasticity in V. cardui. Taken together, I propose that the ancestral species of V. kershawi had similar phenotypic plasticity. Natural selection exploited this plasticity and shaped the present V. kershawi as an independent species, whose specific color-pattern traits are by-products of this adaptation process.

Butterflies (Lepidoptera, Rhopalocera) of West Altai

A total of 176 species of butterflies have been found in West Altai. Their distribution ranges, phenology, biological preferences, and taxonomic structure are analyzed. Numerous Siberian butterfly species from the genera Erebia, Oeneis, Clossiana, Boeberia, and Colias have been found in West Altai which may be accounted for its westernmost position in the mountain system of southern Siberia and very humid climate. At the same time, many western Palaearctic as well as few Middle Asian butterflies have been discovered in West Altai for the first time. West Altai is the region where pairs of sister species which diverged in the Western and Eastern Palaearctic can be found in secondary contact. In this study, a zone of stable secondary sympatry of Melitaea didyma (western element) and M. latonigena (eastern element) as well as that of Maculinea arion (western element) and M. cyanecula (eastern element) has been found. These findings provide the first strong evidence for the distinctness of the species in these sister pairs.

Reproductive isolation in temperate reef fishes

Opportunity and recognition isolation can lead directly to reproductive isolation, the former via divergence in the location and timing of breeding, and the latter via differential mate preferences. We describe the potential significance of these factors in the maintenance of reproductive isolation in a clade of triplefin fishes that occur sympatrically around coastal New Zealand. Specifically, we investigate the roles of spawning time and nesting habitat in promoting opportunity isolation, and of interspecific variation in male body length and breeding colouration in promoting recognition isolation. The triplefin species investigated are reproductively active over several months and show high overlap in breeding times, thus rejecting temporal isolation as a mechanism. Differences in nesting habitats resulted in a reduced probability of encounter between some species, especially between sister-species pairs. Interspecific colour differences generally decreased during the reproductive period, and males of sister-species pairs showed no interspecific colour differences in the ultraviolet light spectrum, thus mate selection based on male colour patterns is unlikely to lead to premating isolation. Finally, males of closely related triplefin species differed in body length, a secondary sexual trait often involved in assortative mating. Thus, spatial differences in nesting habitats reduce the chances of encountering allospecific mates, which may facilitate opportunity isolation and differences in male length, possibly related to species-specific female selection on male body size, may lead to recognition isolation. The combination of limited spatial overlap in nesting habitat and differences in male body size may facilitate species assortative mating in sympatry or parapatry.

Body size and ecological diversification in a sister species pair of triplefin fishes

The effect of body size on spatial resource competition and reproductive isolation was examined in a sister species pair of subtidal triplefin fishes (F. Tripterygiidae) in New Zealand. Ruanoho decemdigitatus and Ruanoho whero have overlapping sympatric distributions and differ in body size, attaining a total length of 12 cm and 9 cm, respectively. R. decemdigitatus was most commonly found in sheltered areas shallower than 5 m, while R. whero was frequently found in sheltered to moderately exposed areas down to 20 m. In sites where the species co-occurred, R. whero was less associated with rock substratum. The effect of body size on substratum use was investigated using laboratory trials based on the field data to test habitat preference and competitive ability in a common setting. Reproductive behaviour was assessed in courtship, mate choice and hybridisation trials. Both species exhibited similar habitat preferences, but large R. decemdigitatus were dominant in inter- and intraspecific contests for the preferred rock habitat, while small R. whero were displaced into less preferred habitats. Courtship behaviour in R. whero was a subset of that displayed by R. decemdigitatus, while no mating behaviour was observed in heterospecific trials. Female R. whero showed a strong preference for smaller males, while female R. decemdigitatus had no preference for male size. Results suggest that body size differences in the Ruanoho pair are consistent with female choice for smaller males in R. whero and competition for habitat in both species. Body size in the Ruanoho species appears to be influenced by conflicting selection pressures that may differ between the species.

The Latitudinal Gradient in Recent Speciation and Extinction Rates of Birds and Mammals

Although the tropics harbor greater numbers of species than do temperate zones, it is not known whether the rates of speciation and extinction also follow a latitudinal gradient. By sampling birds and mammals, we found that the distribution of the evolutionary ages of sister species-pairs of species in which each is the other's closest relative-adheres to a latitudinal gradient. The time to divergence for sister species is shorter at high latitudes and longer in the tropics. Birth-death models fitting these data estimate that the highest recent speciation and extinction rates occur at high latitudes and decline toward the tropics. These results conflict with the prevailing view that links high tropical diversity to elevated tropical speciation rates. Instead, our findings suggest that faster turnover at high latitudes contributes to the latitudinal diversity gradient.

Molecular phylogeny of Pacific Island Colymbetinae: radiation of New Caledonian and Fijian species (Coleoptera, Dytiscidae)

We present a molecular phylogeny and taxonomic review of the Pacific island colymbetine diving beetles, focusing on the Fijian and New Caledonian faunas. Four new species are described: Rhantus monteithi and R. poellerbauerae from New Caledonia, and R. kini and R. bula from Fiji. We also describe the 3rd instar larvae of R. monteithi and R. poellerbauerae spp. nov., assigned to adults using mtDNA sequence data and discuss larval characters in the light of phylogeny. The phylogenetic hypotheses derived from both parsimony and Bayesian inference based on 3508 aligned nucleotides from a combination of mitochondrial (cox1, cob and rrnL‐tRNALeu‐Nad1) and nuclear genes (18S rRNA and H3) reveal a clade comprising R. novaecaledoniae, R. alutaceus, R. pseudopacificus, R. monteithi sp. nov. and R. poellerbauerae sp. nov., which agrees with the R. pacificus group sensu Balke (1993). Carabdytes upin was included within this clade, possibly indicating paraphyly of the genus Rhantus. Rhantus annectens, R. bacchusi, R. supranubicus, R. suturalis, R. simulans, and the Palearctic R. exsoletus, R. latitans and R. bistriatus formed a clade corresponding to the R. suturalis group sensu Balke (2001). Rhantus vitiensis, previously assigned to the R. pacificus group, was included in the R. suturalis clade. We find some support for a scenario where the Pacific was colonized out of the Northern hemisphere only during the past c. 12 million years, rejecting a Gondwanan origin of the morphologically isolated endemics. The new species are all characterized by mtDNA haplotype clusters, the degree of divergence between sister species pairs ranging from 1.3 to 7%, while R. novaecaledoniae individuals from all over New Caledonia apparently form one morphospecies, with moderate genetic diversity (up to 2.3% mtDNA divergence between populations). The sisters R. pollerbauerae sp. nov. + R. monteithi sp. nov. occur sympatrically on Mont Panié but appear ecologically segregated, while the sisters R. vitiensis + R. bula sp. nov. were encountered syntopically on Viti Levu. Comparing genetic and morphological data of Fijian Rhantus and Copelatus diving beetles, we here show that even in island radiations it is not per se possible to know if mitochondrial DNA barcoding would perform well (Rhantus: YES, Copelatus: NO). At the same time we show that fixed cutoff values, as sometimes used to discriminate between barcodes, thus species, might be meaningless. We underpin the importance of morphology for sustainable exploration of global diversity.

MACROEVOLUTIONARY DATA SUGGEST A ROLE FOR REINFORCEMENT IN POLLINATION SYSTEM SHIFTS

Abstract . Reproductive isolation can evolve either as a by-product of divergent selection or through reinforcement. We used the Cape flora of South Africa, known for its high level of pollination specialization, as a model system to test the potential role of shifts in pollination system in the speciation process. Comparative analysis of 41 sisterspecies pairs (representing Geraniaceae, Iridaceae, and Orchidaceae) for which complete pollinator, edaphic, and distribution data are available showed that for sister species with overlapping distribution ranges, pollination system shifts are significantly associated with edaphic shifts. In contrast, there is no significant association between pollination system shifts and edaphic shifts for allopatric sister species. These results are interpreted as evidence for reinforcement.

PHYLOGENETIC ANALYSIS OF THE EVOLUTION OF THE NICHE IN LIZARDS OF THEANOLIS SAGREIGROUP

Recent advances in ecological niche modeling (ENM) algorithms, in conjunction with increasing availability of geographic information system (GIS) data, allow species' niches to be predicted over broad geographic areas using environmental characteristics associated with point localities for a given species. Consequently, the examination of how niches evolve is now possible using a regionally inclusive multivariate approach to characterize the environmental requirements of a species. Initial work that uses this approach has suggested that niche evolution is characterized by conservatism: the more closely related species are, the more similar are their niches. We applied a phylogenetic approach to examine niche evolution during the radiation of Cuban trunk-ground anoles (Anolis sagrei group), which has produced 15 species in Cuba. We modeled the niche of 11 species within this group using the WhyWhere ENM algorithm and examined the evolution of the niche using a phylogeny based on approximately 1500 base pairs of mitochondrial DNA. No general relationship exists between phylogenetic similarity and niche similarity. Examination of species pairs indicates some examples in which closely related species display niche conservatism and some in which they exhibit highly divergent niches. In addition, some distantly related species exhibit significant niche similarity. Comparisons also revealed a specialist-generalist sister species pair in which the niche of one species is nested within, and much narrower than, the niche of another closely related species.

Gis-based niche models reveal unifying climatic mechanisms that maintain the location of avian hybrid zones in a North American suture zone

The existence of suture zones in North America has recently been verified, yet the environmental factors responsible for the maintenance of their structure and position have remained undetermined. The Great Plains suture zone in the US is perhaps the most significant and broadly studied in North America. Numerous avian hybrid zones that cluster in this region have been extensively studied over the last half-century. A primary result of this work is that exogenous factors present in this region have promoted and maintained avian species divergence. Yet, to date the variables most important in the generation and the clustered positioning of these hybrid zones in relation to one another have not been determined. The present study aims to advance our understanding of this North American suture zone by using niche modelling to quantify which environmental variables are most important in its formation and maintenance. Through the generation of fundamental niches for four hybrids and their parental species, similarities linking the hybrid zones were uncovered. The results show that temperature holds this suture zone in position and also suggest that temperature played a primary role in promoting niche differentiation among these sister species pairs during Pleistocene glacial cycles.

THE TEMPO OF AVIAN DIVERSIFICATION: REPLY

THE TEMPO OF AVIAN DIVERSIFICATION: REPLY

MACROEVOLUTIONARY DATA SUGGEST A ROLE FOR REINFORCEMENT IN POLLINATION SYSTEM SHIFTS

Reproductive isolation can evolve either as a by-product of divergent selection or through reinforcement. We used the Cape flora of South Africa, known for its high level of pollination specialization, as a model system to test the potential role of shifts in pollination system in the speciation process. Comparative analysis of 41 sister-species pairs (representing Geraniaceae, Iridaceae, and Orchidaceae) for which complete pollinator, edaphic, and distribution data are available showed that for sister species with overlapping distribution ranges, pollination system shifts are significantly associated with edaphic shifts. In contrast, there is no significant association between pollination system shifts and edaphic shifts for allopatric sister species. These results are interpreted as evidence for reinforcement.

Genetic Divergence between Gopher Rockfish (Sebastes carnatus) and Black and Yellow Rockfish (Sebastes chrysomelas)

The genus Sebastes contains over 110 species, an unusually high level of species diversity for marine fishes. Many of the 70 species that occupy the northeast Pacific Ocean coexist during parts or all of their life cycle. Although allopatric speciation explains much of this diversity, the presence of many closely related species within the same locations suggests that other isolating mechanisms may play a role. Sebastes carnatus and Sebastes chrysomelas are a sympatrically distributed pair of sister species having no morphologically distinguishing characteristics other than color: S. carnatus has pinkish spots on a brown background, and S. chrysomelas has yellow spots on a black background. In this study, seven nuclear microsatellite DNA loci were employed to assess relatedness of 111 S. carnatus and 91 S. chrysomelas sampled from three locations spanning the species' range. Analysis of the seven microsatellite loci provided evidence of genetic divergence between color morphs (FST = 0.046, P < 0.0001). Furthermore, magnitude of genetic divergence between the color morphs was consistent among geographic locations. Divergence between S. carnatus and S. chrysomelas was low relative to that detected among other species within the genus, suggesting that the two morphs represent reproductively isolated incipient species.

The Origin and Radiation of Macaronesian Beetles Breeding in Euphorbia: The Relative Importance of Multiple Data Partitions and Population Sampling

Species-level phylogenies derived from many independent character sources and wide geographical sampling provide a powerful tool in assessing the importance of various factors associated with cladogenesis. In this study, we explore the relative importance of insular isolation and host plant switching in the diversification of a group of bark beetles (Curculionidae: Scolytinae) feeding and breeding in woody Euphor biaspurges. All species in the genus Aphanarthrumare each associated with only one species group of Euphorbia(succulents or one of three different arborescent groups), and the majority of species are endemic to one or several of the Macaronesian Islands. Hence, putative mechanisms of speciation could be assessed by identifying pairs of sister species in a phylogenetic analysis. We used DNA sequences from two nuclear and two mitochondrial genes, and morphological characters, to reconstruct the genealogical relationships among 92 individuals of 25 species and subspecies of Aphanarthrumand related genera. A stable tree topology was highly dependent on multiple character sources, but much less so on wide population sampling. However, multiple samples per species demonstrated one case of species paraphyly, as well as deep coalescence among three putative subspecies pairs. The phylogenetic analyses consistently placed the arborescent breeding and West African--Lanzarote-distributed species A. armatumin the most basal position in Aphanarthrum, rendering this genus paraphyletic with respect to Coleobothrus. Two major radiations followed, one predominantly African lineage of succulent feeding species, and one island radiation associated with arborescent host plants. Sister comparisons showed that most recent divergences occurred in allopatry on closely related hosts, with subsequent expansions obscuring more ancient events. Only 6 out of 24 cladogenetic events were associated with host switching, rendering geographical factors more important in recent diversification.

SPECIATION IN HAWAIIAN ANGIOSPERM LINEAGES: CAUSE, CONSEQUENCE, AND MODE

The biota of Hawaiian Islands is derived entirely from long distance dispersal, often followed by in situ speciation. Species descended from each colonist constitute monophyletic lineages that have diverged to varying degrees under similar spatial and temporal constraints. We partitioned the Hawaiian angiosperm flora into lineages and assessed morphological, ecological, and biogeographic characteristics to examine their relationships to variation in species number (S). Lineages with external bird dispersal (through adhesion) were significantly more species-rich than those with abiotic dispersal, but only weakly more species-rich than lineages with internal bird dispersal (involving fleshy fruits). Pollination mode and growth form (woody vs. herbaceous) had no significant effect on S, in contrast to studies of angiosperm families. S relates positively to the geographic and ecological range size of whole lineages, but negatively to local abundance and mean range sizes of constituent species. Species-rich lineages represent a large proportion of major adaptive shifts, although this appears to be an artifact of having more species. Examination of 52 sister species pairs in numerous lineages provides evidence for allopatric (including peripheral isolates) and parapatric (ecological) modes, with 15 cases of each. Although postspeciational dispersal may obscure these modes in many of the remaining cases, instances of sympatric and hybrid speciation are also discussed. Because speciation is both a consequence and a cause of ecological and biogeographic traits, speciation mode may be integral to relationships between traits. We discuss the role of speciation in shaping the regional species pool.

Cricket Song in Sympatry: Species Specificity of Song without Reproductive Character Displacement in &lt;I&gt;Gryllus rubens&lt;/I&gt;

Previous work with the cryptic sister species pair of field crickets, Gryllus texensis Cade & Otte and Gryllus rubens Scudder, has implicated sexual selection in the speciation process. That study examined reproductive character displacement (RCD) in male song and female preference for song in G. texensis. No evidence of RCD was found. Here, we provide a similar analysis of RCD in G. rubens song and examine the songs of both species from areas of sympatry in an effort to document the species-specificity of song in sympatry and to look for individuals with songs indicative of F1 hybrid status. We 1) find no evidence for RCD in G. rubens song, 2) demonstrate the distinctness of song in sympatry, and 3) document the rarity of songs typical of F1 hybrids.

NEW MITOCHONDRIAL DNA DATA AFFIRM THE IMPORTANCE OF PLEISTOCENE SPECIATION IN NORTH AMERICAN BIRDS

The timing of origin of modern North American bird species in relation to Pleistocene glaciations has long been the topic of significant discussion and disagreement. Recently, Klicka and Zink (1997) and Avise and Walker (1998) enlivened this debate by using calibrated molecular distance values to estimate timing of speciations. Here we use new molecular studies to test their conclusions. Molecular distance values for 39 pairs of proven sister species, 27 of which are based on new data, alter the currently perceived pattern that avian species splits occurred mainly in the Pliocene and early–mid-Pleistocene. Mitochondrial DNA divergence values for this set of taxa showed a skewed distribution pointing toward relatively young speciation times, in contrast to the pattern presented by Klicka and Zink (1997) for 35 sister plus non-sister species pairs. Our pattern was not significantly different from that of Avise and Walker (1998) for “intraspecific phylogroups,” some of which are species. We conclude that the entire Pleistocene, including the last two glacial cycles (<250,000 years ago), was important in speciations of modern North American birds. A substantial number of speciations were both initiated and completed in the last 250,000 years. Simultaneously, many taxa began to diverge in the Pleistocene but their speciations are not yet complete (per Avise and Walker 1998). The suggestion that durations of speciations average two million years is probably a substantial overestimate.

Chromosomal phylogeny of the Drosophila fasciola species subgroup revisited (Diptera, Drosophilidae)

The analysis of polytene chromosomes in 26 strains of seven species in the Drosophila fasciola subgroup, from several locations in Brazil, in addition to strains of two species belonging to the Drosophila mulleri subgroup (D. aldrichi and D. mulleri), enabled us to determine that the 3c inversion found in the latter species differ in one of its break points from that present in the species of the fasciola subgroup. Therefore, a change in the mulleri complex denomination from inversion 3c to inversion 3u is proposed. Accordingly, the fasciola subgroup is no longer a lesser phylogenetic part within the mulleri subgroup. Rather, it is directly related to the likely ancestor of the repleta group, called Primitive I. This information removes the main obstacle to considering the Drosophila fasciola subgroup as an ancestral group within the Drosophila repleta species group, according to the hypothesis of Throckmorton. Our data also support the conclusion that D. onca and D. carolinae are closely related species based on one new inversion in chromosome 4 (4f2), in both species. D. fascioloides and D. ellisoni also form a pair of sister species based on the presence of fusions of chromosomes 2-4 and 3-5. D. rosinae is related only to the likely ancestor of the fasciola subgroup, where the 3c inversion was fixed.