Male recognition of conspecific female chemical cues in a diverse clade of freshwater fishes

Where orangethroat darters (Etheostoma: Ceasia) and rainbow darters (Etheostoma caeruleum) co-occur, males prefer conspecific over heterospecific females. The cues males use to identify conspecific females remain unclear. We conducted behavioral trials to ask whether chemical cues function in conspecific recognition. We found that males from three orangethroat darter species preferentially associate with female scent over a control. Our results support the use of olfaction in conspecific identification in the orangethroat clade and contribute to our understanding of signals that may facilitate species recognition and underlie the evolution of behavioral isolation.     

Recovering cryptic diversity and ancient drainage patterns in eastern North America: historical biogeography of the Notropis rubellus species group (Teleostei: Cypriniformes)

The Central Highlands of North America contain a strikingly diverse assemblage of temperate freshwater fishes and have long been a focus of biogeographic studies. The rosyface shiner complex, Notropis rubellus and related species, is a member of this fauna exhibiting a disjunct highlands distribution occurring in the unglaciated regions of the Central Highlands and glaciated regions of the Central Lowlands. Until recently, N. rubellus was considered a single, widespread species exhibiting geographic variation in morphological characters. However, several studies have revealed that N. rubellus is a multi-species complex with closely related species endemic to drainages within each highland region. We examined genetic variation of the N. rubellus complex using a complete mtDNA cytochrome b gene sequence data set and combined mtDNA and published allozyme data sets. Parsimony and Bayesian analyses of the mitochondrial data set and parsimony analyses of a combined mitochondrial and allozyme data sets were largely consistent. Results of these analyses revealed ancient cryptic diversity within the N. rubellus complex that existed prior to the onset of Pleistocene glaciations. We identified seven strongly supported clades within the N. rubellus complex. Four clades are diagnosed as separate species (N. percobromus, N. rubellus, N. micropteryx and N. suttkusi) and three clades may represent undescribed forms. Relationships among these groups and their biogeographical patterns provided significant inferences on ichthyofaunal distributions in southeastern North America. These include the timing of the origin of the diversity, ancient drainage patterns and barriers to dispersal in the Central Highlands. The observation of increased diversity in N. rubellus suggests there may be greater diversity within other taxa with a similar distribution.     

Male and female contributions to behavioral isolation in darters as a function of genetic distance and color distance

Determining which reproductive isolating barriers arise first between geographically isolated lineages is critical to understanding allopatric speciation. We examined behavioral isolation among four recently diverged allopatric species in the orangethroat darter clade (Etheostoma: Ceasia). We also examined behavioral isolation between each Ceasia species and the sympatric rainbow darter Etheostoma caeruleum. We asked (1) is behavioral isolation present between allopatric Ceasia species, and how does this compare to behavioral isolation with E. caeruleum, (2) does male color distance and/or genetic distance predict behavioral isolation between species, and (3) what are the relative contributions of female choice, male choice, and male competition to behavioral isolation? We found that behavioral isolation, genetic differentiation, and male color pattern differentiation were present between allopatric Ceasia species. Males, but not females, discerned between conspecific and heterospecific mates. Males also directed more aggression toward conspecific rival males. The high levels of behavioral isolation among Ceasia species showed no obvious pattern with genetic distance or male color distance. However, when the E. caeruleum was included in the analysis, an association between male aggression and male color distance was apparent. We discuss the possibility that reinforcement between Ceasia and E. caeruleum is driving behavioral isolation among allopatric Ceasia species.     

Phylogeography and post-glacial colonization patterns of the rainbow darter, Etheostoma caeruleum (Teleostei: Percidae)

Aim To examine the effects of historical climate change and drainage isolation on the distribution of mitochondrial DNA cytochrome b genetic variation within the rainbow darter, Etheostoma caeruleum (Percidae: Etheostomatinae). Location Eastern North American streams including tributaries to the Mississippi River, Great Lakes, Potomac River and Hudson Bay drainages. Methods Parsimony analyses, Bayesian analyses and haplotype networks of mitochondrial DNA sequences. Results Four major clades were recovered from sampled populations of E. caeruleum. Three of four clades are distributed in the western portion of the species’ range (primarily west of the Mississippi River). Samples from this region do not form a monophyletic group, and sequences often vary greatly between samples from adjacent stream systems (up to 7.2% divergence). A basal clade includes samples from the White River system in the Ozark Highlands. The northern Ozarks–upper Midwest clade includes samples from Missouri River tributaries and the upper Midwest (Hudson Bay, upper Mississippi River, and western Lake Michigan drainage). The eastern clade is composed of individuals from the Ohio River, Great Lakes and Potomac River. The Mississippi River corridor clade includes samples from middle and lower Mississippi River tributaries. Main conclusions The four major clades of E. caeruleum are deep allopatric lineages with well‐defined boundaries and have additional phylogeographical structure within each clade. The Ozark Highlands have the greatest levels of diversity relative to distributional area, with marked cytochrome b subdivisions between adjacent stream systems. Samples from previously glaciated areas do not have a subset of the cytochrome b diversity found in unglaciated areas, but four separate source areas are identified based on phylogenetic analyses. Dispersal into previously glaciated areas followed several known glacial outlets and, based on sequence divergence between populations, may have occurred during different glacial or interglacial stages. The disjunct distribution and cytochrome b pattern of E. caeruleum in the Mississippi River corridor clade is consistent with late Pleistocene and Recent changes in the course and characteristics of the middle and lower Mississippi River. Phylogeographical boundaries between clades of E. caeruleum correspond to independent sources of biogeographical information and provide insight into historical stream drainage relationships, post‐glacial colonization and drainage isolation patterns.     

Highest genetic diversity at the northern range limit of the rare orchid Isotria medeoloides

Populations in previously glaciated regions are often genetically depauperate in comparison with populations at lower latitudes, due either to bottlenecks experienced in post-glacial colonization or to contemporary genetic drift in small, peripheral populations. Populations of the rare self-fertilizing North American orchid Isotria medeoloides are largest in the previously glaciated region near the northern range limit, allowing us to examine the role of historical versus contemporary processes in determining population genetic diversity and structure. If contemporary processes predominate, genetic diversity should increase with increasing census size. In contrast, if sequential bottlenecks associated with colonization are paramount, diversity should decrease with latitude and be relatively insensitive to census size. We genotyped 299 individuals from 20 populations at four variable microsatellite loci to contrast genetic diversity and structure for populations in previously glaciated regions versus previously unglaciated regions. Populations were highly inbred (F=0.95) and highly differentiated (R(ST)=0.485). Across all sampled populations, genetic diversity decreased and genetic differentiation increased with declining population size. Small southern populations were especially differentiated and genetically depauperate. In the glaciated part of the range, genetic diversity increased as populations approached the northern range limit, demonstrating the centrality of contemporary processes for this post-glacial colonist.     

Male orangethroat darters,Etheostoma spectabile, do not prefer larger females

Synopsis Male orangethroat darters,Etheostoma spectabile, did not show a preference for larger females as measured by the number of matings or time until mating in a field enclosure experiment. The lack of male preference for female size may be due to the male-biased sex ratio at the site (seven males per female) or to low variation in the number of eggs deposited per spawning.     

THE ZOOGEOGRAPHY AND CENTERS OF ORIGIN OF THE CRAYFISH SUBGENUS PROCERICAMBARUS (DECAPODA: CAMBARIDAE)

The Central Highlands region in the central United States is a taxonomically diverse region with a high incidence of stream endemism. Based on the distributions of the diverse ichthyofauna in the region, a pre-Pleistocene pattern of diversity due to vicariant events has been proposed to explain high levels of endemism and species richness. We tested this hypothesis using crayfish phylogenies and distributional patterns for species distributed in the Central Highlands region. We concluded that both pre-Pleistocene and Pleistocene hypotheses are compatible with the crayfish distributions and these distributions are likely due to a combination of both vicariant and dispersal events. Furthermore, we suggest a Pleistocene center of origin for the crayfish subgenus Procericambarus within the Ozark region and a pre-Pleistocene center of origin for the genus Orconectes within the Eastern Highlands region.     

Comparative riverscape genomics of the rainbow darter (Etheostoma caeruleum) in glaciated and unglaciated environments

Periodic glaciation during the Quaternary period shaped the contemporary riverscape and distribution of freshwater fishes in the Mississippi River drainage of central North America. The rainbow darter (Etheostoma caeruleum) is a member of this ichthyofauna and has a disjunct distribution in glaciated and unglaciated environments west of the Mississippi River. Based on glacial history of the region, there are different expectations on the observed spatial genetic structure of populations in these environments. The aim of this study was to utilize genome‐wide SNP data to compare the population genomic structure of the rainbow darter in river networks with disparate glacial histories; the Volga River in the glaciated upper Mississippi River basin and the Meramec River in the unglaciated Ozark Plateau. Individuals were sampled from localities within each river system at distances dictated by the organismal life history and habitat preferences. Riverscape analyses were performed on three datasets: total combined localities of both rivers and one for each river independently. The results revealed a lasting influence of historic glaciation on the population genomic structure of rainbow darter populations. There was evidence of population expansion into the glaciated northern region following glacial retreat. The population genetic signature within the Volga River did not fit expectations of the stream hierarchy model, but revealed a pattern of repeated colonization and extirpation due to cyclic glaciation. The population within the unglaciated Meramec River adhered to the stream hierarchy model, with a directional order of genetic diversity based on the life history and habitat preferences of the species. These results demonstrate the importance of considering the geologic and climatic history of a region as well as the life history of an organism when interpreting spatial genetic patterns.     

Refugia in the Cordilleran ice sheet of western North America: chloroplast DNA diversity in the Arctic–alpine plant Oxyria digyna

Aim  Late Pleistocene ice sheets are thought to have covered most of western Canada, including all of British Columbia (BC). We examine patterns of genetic variation in an Arctic–alpine plant to evaluate the possibility of full glacial refugia within the area covered by the Cordilleran ice sheet (CIS) and to uncover post-glacial migration routes.
Location  Western North America.
Methods  We sampled 1030 individuals of the Arctic–alpine plant Oxyria digyna from 117 populations distributed over much of its range in western and northern North America. DNA haplotypes were identified using restriction site analysis of two chloroplast DNA intergene spacer regions, psb A- trn H and trn T-L. We examined the geographical distribution of haplotype diversity in relation to latitude, and also compared various indices of diversity in putatively glaciated and unglaciated regions. Patterns of migration were inferred using nested clade analysis.
Results  We detected a total of 20 haplotypes. High haplotype diversity was found in Beringia, in unglaciated western USA, and in northern BC at 57–59° N, well within the accepted limits of the CIS. Ancestral haplotypes were also centred in northern BC.
Main conclusions  High genetic diversity of Oxyria digyna is expected in unglaciated regions, but unexpected in northern BC if British Columbia was entirely covered by ice during the late Pleistocene. Our observations suggest the presence of unglaciated areas providing late Pleistocene refugia in northern BC. Such refugia would have important implications for the origins and migrations of many plant and animal species in north-western North America.     

Microsatellite DNA markers for the rainbow darter,Etheostoma caeruleum (Percidae), and their potential utility for other darter species

The rainbow darter Etheostoma caeruleum is a small fish in the perch family (Percidae) that is adapted to fast‐flowing streams in eastern North America. It is relatively sensitive to habitat degradation and is widely used as a sentinel of stream condition. To provide a complementary tool for assessing the integrity of stream ecosystems, 16 highly polymorphic tetranucleotide microsatellite markers were identified for these darters. Between four and 16 loci were found to be useful in five congeneric species. These markers will be useful for characterizing population genetic structure and diversity of rainbow darters and related fishes.     

Reproductive isolation between two darter species is enhanced and asymmetric in sympatry

Robust reproductive isolation was found between the rainbow darter Etheostoma caeruleum and the orangethroat darter Etheostoma spectabile, as more offspring were produced when conspecific males and females were crossed as compared with heterospecific crosses. Furthermore, fewer eggs resulted from heterospecific crosses involving sympatric E. spectabile females than those using allopatric E. spectabile females, while a similar pattern was not observed in heterospecific crosses using E. caeruleum females. These results suggest that reinforcement, i.e. selection for pre‐zygotic reproductive barriers driven by reduced hybrid fitness, may have contributed to the evolution and maintenance of reproductive barriers between these potentially hybridizing species in sympatry.     

Genetic consequences of glacial survival: the late Quaternary history of balsam poplar (Populus balsamifera L.) in North America

Aim Beringia, the unglaciated region encompassing the former Bering land bridge, as well as the land between the Lena and Mackenzie rivers, is recognized as an important refugium for arctic plants during the last ice age. Compelling palaeobotanical evidence also supports the presence of small populations of boreal trees within Beringia during the Last Glacial Maximum. The occurrence of balsam poplar (Populus balsamifera) in Beringia provides a unique opportunity to assess the implications of persistence in a refugium on present‐day genetic diversity for this boreal tree species. Location North America. Methods We sequenced three variable non‐coding regions of the chloroplast genome (cpDNA) from 40 widely distributed populations of balsam poplar across its North American range. We assessed patterns of genetic diversity, geographic structure and historical demography between glaciated and unglaciated regions of the balsam poplar’s range. We also utilized a coalescent model to test for divergence between regions. Results Levels of genetic diversity were consistently greater for populations at the southern margin (θ_W = 0.00122) than in the central (θ_W = 0.00086) or northern (θ_W = 0.00034) regions of the current distribution of balsam poplar, and diversity decreased with increasing latitude (R² = 0.49, P < 0.01). We detected low, but significant, structure (F_CT = 0.05, P = 0.05), among regions of P. balsamifera’s distribution. The cpDNA genealogy was shallow, however, showing an absence of highly differentiated chloroplast haplotypes. Coalescent analyses supported a model of divergence between the southern ice margin and the northern unglaciated region of balsam poplar’s distribution, but analyses of other regional comparisons did not converge. Main conclusions The palaeobotanical record supports the presence of a Beringian refugium for balsam poplar, but we were unable to definitively identify the presence of known refugial populations based on genetic data alone. Balsam poplar populations from Beringia are not a significant reservoir of cpDNA diversity today. Unique alleles that may have been present in the small, isolated populations that survived within Beringia were probably lost through genetic drift or swamped by post‐glacial, northward migration from populations south of the ice sheets.     

Phylogeography of the bigeye chub Hybopsis amblops (Teleostei: Cypriniformes): early Pleistocene diversification and post‐glacial range expansion

The bigeye chub, Hybopsis amblops, is a member of the Central Highlands ichthyofauna of eastern North America. Phylogenetic analyses of the H. amblops species group based on a 1059 bp fragment of the mitochondrial DNA cytochrome b gene did not recover a monophyletic group. The inclusion of Hybopsis hypsinotus in the species complex is questionable. Within H. amblops, five strongly supported clades were identified; two clades containing haplotypes from the Ozark Highlands and three clades containing haplotypes from the Eastern Highlands and previously glaciated regions of the Ohio and Wabash River drainages. Estimates of the timing of divergence indicated that prior to the onset of glaciation, vicariant events separated populations east and west of the Mississippi River. East of the Mississippi River glacial cycles associated with the blocking and rerouting of the Teays River system caused populations to be pushed southward into refugia of the upper Ohio River. Following the most recent Wisconsinan glaciation, populations expanded northward into previously glaciated regions and southward into the Cumberland River drainage. In the Ozarks, west of the Mississippi River, isolation of clades appears to be maintained by the lack of stream capture events between the upper Arkansas and the White River systems and a barrier formed by the Arkansas River.     

The coastal-disjunct mesic flora in the inland Pacific Northwest of USA and Canada: refugia, dispersal and disequilibrium

Aim Understanding the history of the mesic‐adapted plant species of eastern British Columbia and northern Idaho, disjunct from their main coastal distribution, may suggest how biotas reorganize in the face of climate change and dispersal barriers. For different species, current evidence supports establishment of the disjunction via an inland glacial refugium, via recent dispersal from the coast, or via a combination of both. In this study, the modern distributions of the coastal‐disjunct vascular plants are analysed with respect to modern climate to examine how refugia and/or dispersal limitation control regional patterns in species richness. Location North‐west North America. Methods The distributions of nine tree and 58 understorey species with a coastal‐disjunct pattern were compiled on a 50‐km grid. The relationship between species richness and an estimate of available moisture was calculated separately for formerly glaciated and unglaciated portions of the coastal and inland regions. Growth habit and dispersal mode were assessed as possible explanatory variables for species distributions. Results Species richness shows a strong relationship to climate in coastal‐unglaciated areas but no relationship to climate in inland‐glaciated areas. In inland‐glaciated areas, richness is c. 70% lower than that expected from climate. Species with animal‐dispersed seeds occupy a larger portion of coastal and inland regions than species with less dispersal potential. Main conclusions Modern patterns of diversity are consistent with both refugia and dispersal processes in establishing the coastal‐disjunct pattern. The inland glacial refugium is marked by locally high diversity and several co‐distributed endemics. In the inland‐glaciated area, dispersal limitation has constrained diversity despite the nearby refugia. Onset of mesic climate within only the last 3000 years and the low dispersal capacity of many species in the refugium may explain this pattern. This study suggests that vascular plant species will face significant challenges responding to climate change on fragmented landscapes.     

Isozyme diversity in Iris Cristata and the threatened glacial endemic I. Lacustris (Iridaceae)

Iris cristata and I. lacustris differ markedly in geographic distribution, glacial history of current ranges, and ecology. We hypothesized that I. cristata, a widespread species of unglaciated regions of eastern North America, would exhibit genetic diversity typical of other widespread plant species, whereas the threatened I. lacustris, which occupies glaciated habitats on Great Lakes shorelines, would display little genetic variation. Iris lacustris lacked detectable polymorphisms in 18 isozyme loci, although we found evidence of possible incomplete gene silencing in four additional loci in some populations. In contrast, I. cristata was polymorphic at 73% of 15 loci examined, with an average of three alleles per locus. Genetic diversity (H_e) was 0.231. All species-level and population-level estimates of genetic diversity were higher than averages for plants having comparable life history traits. Nearly 98% of the total genetic diversity in I. cristata was apportioned within populations, and heterozygosity and fixation estimates suggest a high level of outcrossing in this species (t = 1.265). The long-lived perennial habit and high outcrossing rate in stable populations are proposed as factors contributing to high genetic diversity in I. cristata. The data are consistent with an hypothesis of a recent origin of I. lacustris from a very limited I. cristata gene pool exacerbated by repeated bottlenecks and founder effects as I. lacustris populations were displaced by lake-level changes over the past 11 000 yr.     

Timing of clade divergence and discordant estimates of genetic and morphological diversity in the Slender Madtom,Noturus exilis (Ictaluridae)

Phylogeographic relationships, the timing of clade diversification, and the potential for cryptic diversity in the Slender Madtom, Noturus exilis, was investigated using mitochondrial Cyt b, nuclear RAG2, shape analysis, and meristic and pigmentation data. Three well-supported and deeply divergent clades were recovered from analyses of genetic data: Little Red River (White River drainage) clade, Arkansas + Red River (Mississippi River) clade, and a large clade of populations from the rest of the range of the species. Recovered clades showed little to no diagnostic morphological differences, supporting previous hypotheses of morphological conservatism in catfishes, and indicating morphology may commonly underestimate diversity in this group of fishes. The Little Red River clade is the most distinct lineage of N. exilis with 11 POM pores (vs. 10 in other populations) and unique Cyt b haplotypes and RAG 2 alleles. However, treating it as a species separate from N. exilis would imply that the other major clades of N. exilis are more closely related to one another than they are to the Little Red River clade, which was not supported.The UCLN age estimate for Noturus was 23.9 mya (95% HPD: 13.49, 35.43), indicating a late Oligocene to early Miocene origin. The age of N. exilis was estimated as late Miocene at 9.7 mya (95% HPD: 5.32, 14.93). Diversification within the species spanned the late Miocene to mid-Pleistocene. The largest clade of N. exilis, which dates to the late Miocene, includes populations from the unglaciated Eastern and Interior Highlands as well as the previously glaciated Central Lowlands. Diversification of this clade coincides with a drastic drop in sea-level and diversification of other groups of Central Highlands fishes (Centrarchidae and Cyprinidae). Sub-clades dating to the Pleistocene show that northern populations occurring in previously glaciated regions resulted from dispersal from populations in the Ozarks up the Mississippi River following retreat of the Pleistocene glaciers. Pre-Pleistocene vicariance, such as drainage pattern changes of the Mississippi River, also played a prominent role in the history of the species. The incorporation of a temporal estimate of clade diversification revealed that in some instances, phylogeographic breaks shared with other aquatic species were best explained by different or persistent vicariant events through time, rather than a single shared event.     

Spatial extent of analysis influences observed patterns of population genetic structure in a widespread darter species (Percidae)

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Microhabitat partitioning in a diverse assemblage of darters in the Allegheny River system

Synopsis Habitat partitioning among eleven species of darters (Percidae: Etheostomatini) from the Allegheny River system was studied through underwater observation. Percina caprodes and Percina copelandi showed consistent segregation from Etheostoma by occupying deeper habitats. Substrate size, depth, and water velocity were important variables by which Etheostoma species segregated. Analysis of niche breadth values indicated that species differed widely in their degree of specialization in habitat use; based on the variables measured, Etheostoma zonale was a habitat generalist whereas Etheostoma camurum, Etheostoma tippecanoe, and Percina caprodes tended towards habitat specialization. Habitat segregation appears to be an important mechanism allowing the coexistence of these closely related and ecologically similar species. Microhabitat quantification on a fine scale was important in discovering habitat differences in this diverse system.     

Indirect food web interactions increase growth of an algivorous stream fish

1. We tested the hypothesis that indirect food web interactions between some common, invertivorous fishes and their prey would positively affect growth of an algivorous fish species. Specifically, we predicted that orangethroat darter (Etheostoma spectabile) would increase periphyton biomass via a top‐down pathway, indirectly enhancing growth of the algivorous central stoneroller minnow (Campostoma anomalum). Moreover, we predicted that sand shiner (Notropis stramineus) would increase periphyton biomass via a bottom‐up pathway and indirectly enhance growth of the stoneroller minnow. 2. In an 83‐day experiment in large, outdoor, stream mesocosms, we stocked two fish species per mesocosm (stoneroller and either darter or shiner), estimated the effects of the invertivorous and grazing fishes on periphyton biomass and estimated growth of the algivorous fish. 3. The darter consumed grazing invertebrates, indirectly increasing periphyton biomass. The shiner consumed terrestrial insects as predicted, but it did not affect periphyton biomass. 4. In support of our hypothesis, the darter indirectly enhanced stoneroller growth. As predicted, stonerollers consumed the increased periphyton in streams with darters, resulting in greater growth, condition and gut fullness compared to streams without darters. No indirect interaction was observed between stonerollers and shiners. 5. Our study suggests that some invertivorous fish species can positively affect growth of algivorous fishes through indirect food web interactions. Thus, in stream communities, it is possible that the loss of a single, invertivorous fish taxon could have negative consequences on algivorous fish populations via the removal of positive indirect food web interactions.     

Ecological and evolutionary consequences of early ontogenies of darters (Etheostomatini)

Synopsis The ecological classification of fishes into reproductive guilds is based on the premises that (1) reproductive styles and early ontogeny are closely related, and (2) both are correlated with the ecology of a species. A comparison of early ontogenies of logperch (Percina caprodes), rainbow darter (Etheostoma caeruleum), and fantail darter (E. flabellare) confirmed these premises, and provided possible explanations for diversity within the Etheostomatini. Young logperch have limited vitelline circulation, hatch while still poorly developed, and therefore must drift from oxygen rich lotic habitats to lentic habitats where small planktonic prey are available. Young rainbow and fantail darters have extensive vitelline plexuses, are well developed at transition to first feeding, and begin feeding on aquatic insects. Thus there is no necessity for a drift interval. As a result, the latter species are adapted for stream life. Interspecific differences in reproductive styles and early ontogenies may have contributed to speciation of darters by allowing partitioning of breeding sites and food resources for young. In addition, reduced drift dispersal and small stream habitation may have indirectly contributed to speciation by reducing genetic exchange among populations.