PLANT RESPONSES TO CLIMATE IN THE CAPE FLORISTIC REGION OF SOUTH AFRICA: EVIDENCE FOR ADAPTIVE DIFFERENTIATION IN THE PROTEACEAE

Local adaptation along environmental gradients may drive plant species radiation within the Cape Floristic Region (CFR), yet few studies examine the role of ecologically based divergent selection within CFR clades. In this study, we ask whether populations within the monophyletic white protea clade (Protea section Exsertae, Proteaceae) differ in key functional traits along environmental gradients and whether differences are consistent with local adaptation. Using seven taxa, we measured trait–environment associations and selection gradients across 35 populations of wild adults and their offspring grown in two common gardens. Focal traits were leaf size and shape, specific leaf area (SLA), stomatal density, growth, and photosynthetic rate. Analyses on wild and common garden plants revealed heritable trait differences that were associated with gradients in rainfall seasonality, drought stress, cold stress, and less frequently, soil fertility. Divergent selection between gardens generally matched trait–environment correlations and literature‐based predictions, yet variation in selection regimes among wild populations generally did not. Thus, selection via seedling survival may promote gradient‐wide differences in SLA and leaf area more than does selection via adult fecundity. By focusing on the traits, life stages, and environmental clines that drive divergent selection, our study uniquely demonstrates adaptive differentiation among plant populations in the CFR.     

Geological history and oceanography of the Indo‐Malay Archipelago shape the genetic population structure in the false clown anemonefish (Amphiprion ocellaris)

Like many fishes on coral reefs, the false clown anemonefish, Amphiprion ocellaris, has a life history with two different phases: adults are strongly site attached, whereas larvae are planktonic. Therefore, the larvae have the potential to disperse, but the degree of dispersal potential depends primarily on the period of the larval stage, which is only 8–12 days in A. ocellaris. In this study, we investigated the genetic population structure and gene flow in A. ocellaris across the Indo‐Malay Archipelago by analysing a fragment of the mitochondrial control region. Population genetic analysis, using amova , revealed a significant and high overall Φ_ST‐value of 0.241 (P < 0.001), clearly showing limited gene flow. Haplotype network analysis detected eight distinct clades corresponding mainly to different geographical areas, which were most probably separated during sea level low stands in the Pleistocene. The distribution of the clades among the different populations indicated slow partial re‐mixing mainly in the central region of the archipelago. Major surface currents seem to facilitate larval dispersal, indicated by higher connectivity along major surface currents in the region (e.g. Indonesian Throughflow). Four main groups were found by the hierarchical amova within the archipelago. These different genetic lineages should be managed and protected as separate ornamental fishery stocks and resource contributing to the genetic diversity of the area. Regarding the high diversity and the differentiation among areas within the Indo‐Malay Archipelago of A. ocellaris populations, the centre‐of‐origin theory is supported to be the main mechanism by which the high biodiversity evolved in this area.     

Geographical affinities of the Cape flora, South Africa

Aim The flora characteristic of the Cape Floristic Region (CFR) is dominated by a relatively small number of clades that have been proposed as ‘Cape clades’. These clades have variously been suggested to have African or Austral affinities. Here we evaluate the support for these conflicting hypotheses. In addition, we test the hypothesis that these clades share a common time of differentiation from their geographical neighbours. Location The Cape Floristic Region, South Africa Methods We use both published and unpublished phylogenetic information to investigate the geographical sister areas of the Cape clades as well as the timing and the direction of biogeographical disjunctions. Results Almost half of the Cape clades for which unambiguous sister areas could be established show a trans‐Indian Ocean disjunction. The earliest trans‐Indian Ocean disjunction dates from 80 Ma. Other disjunctions date from various times in the Cenozoic, and we suggest that the process of recruiting lineages into the Cape flora might be ongoing. Relatively few Cape clades show a sister relationship with South America and tropical Africa, despite their relative geographical proximity. Numerous Cape clades contain species also found on tropical African mountains; in all cases tested, these species are shown to be embedded within the Cape clades. While many Cape clades show a relationship with the Eurasian temperate flora, this is complicated by their presence in tropical Africa. The single case study addressing this to date suggests that the Cape clade is nested within a European grade. Main conclusions Although many Cape clades show Austral rather than African relationships, there are numerous other patterns suggestive of a cosmopolitan flora. This spatial variation is echoed in the temporal data, from which, although there is wide variance around the dates of disjunctions, it is clear the Cape flora has been assembled over a long time period. There is no simple hypothesis that can account for the geographical sources of the currently distinctive Cape flora. The phylogenetic positions of Afromontane members of Cape clades suggest a history of dispersal from the CFR, rather than the reverse.     

Patterns and processes underlying evolutionary significant units in the Platypleura stridula L. species complex (Hemiptera: Cicadidae) in the Cape Floristic Region, South Africa

Cicadas have been shown to be useful organisms for examining the effects of distribution, plant association and geographical barriers on gene flow between populations. The cicadas of the Platypleura stridula species complex are restricted to the biologically diverse Cape Floristic Region (CFR) of South Africa. They are thus an excellent study group for elucidating the mechanisms by which hemipteran diversity is generated and maintained in the CFR. Phylogeographical analysis of this species complex using mitochondrial DNA Cytochrome Oxidase I (COI) and ribosomal 16S sequence data, coupled with preliminary morphological and acoustic data, resolves six clades, each of which has specific host-plant associations and distinct geographical ranges. The phylogeographical structure implies simultaneous or near-simultaneous radiation events, coupled with shifts in host-plant associations. When calibrated using published COI and 16S substitution rates typical for related insects, these lineages date back to the late Pliocene - early Pleistocene, coincident with vegetation change, altered drainage patterns and accelerated erosion in response to neotectonic crustal uplift and cyclic Pleistocene climate change, and glaciation-associated changes in climate and sea level.     

Environmental niche conservatism explains the accumulation of species richness in Mediterranean‐hotspot plant genera

The causes of exceptionally high plant diversity in Mediterranean‐climate biodiversity hotspots are not fully understood. We asked whether a mechanism similar to the tropical niche conservatism hypothesis could explain the diversity of four large genera (Protea, Moraea, Banksia, and Hakea) with distributions within and adjacent to the Greater Cape Floristic Region (South Africa) or the Southwest Floristic Region (Australia). Using phylogenetic and spatial data we estimated the environmental niche of each species, and reconstructed the mode and dynamics of niche evolution, and the geographic history, of each genus. For three genera, there were strong positive relationships between the diversity of clades within a region and their inferred length of occupation of that region. Within genera, there was evidence for strong evolutionary constraint on niche axes associated with climatic seasonality and aridity, with different niche optima for hotspot and nonhotspot clades. Evolutionary transitions away from hotspots were associated with increases in niche breadth and elevated rates of niche evolution. Our results point to a process of “hotspot niche conservatism” whereby the accumulation of plant diversity in Mediterranean‐type ecosystems results from longer time for speciation, with dispersal away from hotspots limited by narrow and phylogenetically conserved environmental niches.     

Evolutionary Drivers of Diversification and Distribution of a Southern Temperate Stream Fish Assemblage: Testing the Role of Historical Isolation and Spatial Range Expansion

This study used phylogenetic analyses of mitochondrial cytochrome b sequences to investigate genetic diversity within three broadly co-distributed freshwater fish genera (Galaxias, Pseudobarbus and Sandelia) to shed some light on the processes that promoted lineage diversification and shaped geographical distribution patterns. A total of 205 sequences of Galaxias, 177 sequences of Pseudobarbus and 98 sequences of Sandelia from 146 localities across nine river systems in the south-western Cape Floristic Region (South Africa) were used. The data were analysed using phylogenetic and haplotype network methods and divergence times for the clades retrieved were estimated using *BEAST. Nine extremely divergent (3.5–25.3%) lineages were found within Galaxias. Similarly, deep phylogeographic divergence was evident within Pseudobarbus, with four markedly distinct (3.8–10.0%) phylogroups identified. Sandelia had two deeply divergent (5.5–5.9%) lineages, but seven minor lineages with strong geographical congruence were also identified. The Miocene-Pliocene major sea-level transgression and the resultant isolation of populations in upland refugia appear to have driven widespread allopatric divergence within the three genera. Subsequent coalescence of rivers during the Pleistocene major sea-level regression as well as intermittent drainage connections during wet periods are proposed to have facilitated range expansion of lineages that currently occur across isolated river systems. The high degree of genetic differentiation recovered from the present and previous studies suggest that freshwater fish diversity within the south-western CFR may be vastly underestimated, and taxonomic revisions are required.     

A densely sampled ITS phylogeny of the Cape flagship genus Erica L. suggests numerous shifts in floral macro-morphology

Erica L. is the largest of the ‘Cape’ clades that together comprise around half of the disproportionately high species richness of the Cape Floristic Region (CFR) of South Africa. Around 840 species of Erica are currently recognised, C.680 of which are found in the CFR, the rest distributed across the rest of Southern Africa, the highlands of Tropical Africa and Madagascar, and Europe. Erica is taxonomically well documented, but very little is known about species-level relationships. We present the first densely sampled phylogenetic analysis of Erica, using nuclear ribosomal DNA sequences (internal transcribed spacers; ITS) of c. 45% of the species from across the full geographic range of the genus, both Calluna and Daboecia (Ericeae; monotypic genera and putative sister groups of Erica), and further Ericoideae outgroups. Our results show both morphological and geographic coherence of some clades, but numerous shifts in floral macro-morphology as represented by variation in individual morphological characters and pollination syndromes. European Ericeae is a paraphyletic grade subtending a monophyletic African/Malagasy Erica. Given the limited resolution of this single gene tree, more data are needed for further conclusions. Clades are identified that will serve as an effective guide for targeted sampling from multiple linkage groups.     

The Greater Cape Floristic Region

Aim The Cape Floristic Region (CFR) (Cape Floristic Kingdom) is currently narrowly delimited to include only the relatively mesic Cape fold mountains and adjacent intermontane valleys and coastal plains. We evaluate the floristic support for expanding the delimitation to include the whole winter‐rainfall area (arid and mesic climates) into a Greater CFR. Location Southern Africa, particularly the south‐western tip. Methods The initial divisive hierarchical classification analysis twinspan used the presence/absence of vascular plant genera to obtain major floristic groupings in southern Africa. For the more detailed analyses, we scored the flora as present/absent within a set of centres, among which the floristic relationships were investigated (agglomerative methods, upgma and minimum spanning trees). These analyses were conducted with species, genera and families separately. The centres were grouped into five regions. The species richness and endemism was calculated for the centres, regions and combination of regions. The dominant floristic components of each region were sought by calculating the percentage contribution of each family to the flora. Results The divisive method showed that the winter‐rainfall areas are floristically distinct from the rest of southern Africa. The species‐ and generic‐level analyses revealed five regions: CFR, Karoo Region, Hantam‐Tanqua‐Roggeveld Region, Namaqualand Region and Namib‐Desert Region. The CFR has the highest endemism and richness. However, the combination of the CFR, the Hantam‐Tanqua‐Roggeveld Region and the Namaqualand Region results in a higher total endemism. Combined, these three regions almost match the region delimited by the twinspan analysis, and together constitute the Greater CFR. Main conclusions The CFR constitutes a valid floristic region. This is evident from the endemism and the distinctive composition of the flora. However, the total endemism is higher for the whole winter‐rainfall area, and this supports the recognition of the larger unit. If floristic regions are to be delimited only on endemism, then the Greater CFR is to be preferred. If floristic regions are delimited on the composition of their floras at family level, then the support for such a grouping is weaker.     

Was it an explosion? Using population genetics to explore the dynamics of a recent radiation within Protea (Proteaceae L.)

Adaptive radiations likely underlie much of the world’s diversity, especially that of hyper‐diverse regions. They are usually characterized by a burst of speciation early in their evolutionary history, a pattern which can be detected using population genetic tools. The Cape Floristic Region (CFR) of southwestern South Africa is home to many spectacular plant radiations. Here, we investigate the white proteas (Protea section Exsertae), a typical CFR radiation, to determine if it demonstrates the burst of speciation associated with adaptive radiations in recent models. Inferences from individual assignment, tree‐based population relationships, and pairwise F‐statistics based on 10 microsatellite loci reveal that while the white proteas radiated recently they did not radiate explosively. In addition, we found evidence that there is little gene flow between sampled populations of most species. Taken together, these results demonstrate that within a small clade, the processes underlying the radiation are different from those envisioned by current models of adaptive radiation and suggest that geographical isolation could have played a role in the diversification of the group. Our study implicates both adaptive and non‐adaptive processes in the evolution of botanical diversity of the CFR.     

Historical abiotic events or human‐aided dispersal: inferring the evolutionary history of a newly discovered galaxiid fish

Range expansion of obligate freshwater fishes in the Cape Floristic Region (CFR) of South Africa has mostly been attributed to river capture events and confluence of rivers following sea‐level regression. The role of low drainage divides and interbasin water transfers has received less attention. This study analyzed mitochondrial and nuclear DNA sequences to assess the processes that could have influenced the phylogeographic patterns of a newly discovered lineage of Galaxias zebratus (hereafter Galaxias zebratus “Joubertina”) that occurs across two currently isolated river systems close to the Joubertina area in the eastern CFR. Results from both analyses revealed that observed genetic differentiation cannot be explained by isolation between the two river systems. No genetic differentiation was found between the Krom River system and a population from one of the Gamtoos tributaries. Shallow genetic differentiation was found between the Krom and the other Gamtoos populations. Historical river capture events and sea‐level changes do not explain the present distribution of Galaxias zebratus “Joubertina” across the Krom and Gamtoos River systems. Interbasin dispersal during pluvial periods, recent river capture, or recent human‐mediated translocation seems to be the most plausible explanations.     

Diversification rate shifts in the Cape Floristic Region: The right traits in the right place at the right time

Species diversity patterns are the product of diversification rate variation, but the factors influencing changes in diversification rates are poorly known. Radiation is thought to be the result of ecological opportunity: the right traits in the right environment at the right time. We test this in the Cape Floristic Region (CFR) of South Africa, in which pyrophytic heathland (fynbos) and non-pyrophytic Afromontane forest occur interdigitated. We infer transitions from forest to fynbos in three Cape clades (Penaeaceae, Phyliceae and Diosmeae) and test if they are associated with diversification rate shifts and the evolution of functional traits linked to fire, high insolation and seasonal drought. We estimate diversification rate shifts using maximum likelihood and use phylogenetic comparative methods to show that forest to fynbos shifts were associated with decreases in leaf area and specific leaf area and preceded or coincided with increases in diversification rates. Furthermore, we show that Penaeaceae, Phyliceae and Diosmeae species are typical members of their vegetation types in terms of their traits. The diversification rate shifts of Penaeaceae and Phyliceae are dated to the Miocene, when postulated aridification-driven changes in the CFR fire regimes may have triggered expansion of the fynbos at the cost of forest, providing an ecological opportunity for the diversification of fynbos lineages.     

Genetic population structure of the net-winged midge, Elporia barnardi (Diptera: Blephariceridae) in streams of the south-western Cape, South Africa: implications for dispersal

SUMMARY 1. The net‐winged midges (Diptera: Blephariceridae), with highly specific habitat requirements and specialised morphological adaptations, exhibit high habitat fidelity and a limited potential for dispersal. Given the longitudinal and hierarchical nature of lotic systems, along with the geological structure of catchment units, we hypothesise that populations of net‐winged midge should exhibit a high degree of population sub‐structuring. 2. Sequence variation in the cytochrome c oxidase subunit I (COI) region of the mitochondrial DNA (mtDNA) was examined to determine patterns of genetic variation and infer historical and contemporary processes important in the genetic structuring of populations of Elporia barnardi. The DNA variation was examined at sites within streams, between streams in the same range, and between mountain ranges in the south‐western Cape of South Africa. 3. Twenty‐five haplotypes, 641 bp in length, were identified from the 93 individuals sampled. A neighbour‐joining tree revealed two highly divergent clades (～5%) corresponding to populations from the two mountain ranges. A number of monophyletic groups were identified within each clade, associated with individual catchment units. 4. The distribution of genetic variation was examined using analysis of molecular variance (amova ). This showed most of the variation to be distributed among the two ranges (～80%), with a small percentage (～15%) distributed among streams within each range. Similarly, variation among streams on Table Mountain was primarily distributed among catchment units (86%). A Mantel's test revealed a significant relationship between genetic differentiation and geographical distance, suggesting isolation by distance (P < 0.001). 5. Levels of sequence divergence between the two major clades, representing the two mountain ranges, are comparable with those of some intra‐generic species comparisons. Vicariant events, such as the isolation of the Peninsula mountain chain and Table Mountain, may have been important in the evolution of what is now a highly endemic fauna. 6. The monophyletic nature of the catchment units suggests that dispersal is confined to the stream environment and that mountain ridges provide effective physical barriers to dispersal of E. barnardi.     

Dated Plant Phylogenies Resolve Neogene Climate and Landscape Evolution in the Cape Floristic Region

In the context of molecularly-dated phylogenies, inferences informed by ancestral habitat reconstruction can yield valuable insights into the origins of biomes, palaeoenvironments and landforms. In this paper, we use dated phylogenies of 12 plant clades from the Cape Floristic Region (CFR) in southern Africa to test hypotheses of Neogene climatic and geomorphic evolution. Our combined dataset for the CFR strengthens and refines previous palaeoenvironmental reconstructions based on a sparse, mostly offshore fossil record. Our reconstructions show remarkable consistency across all 12 clades with regard to both the types of environments identified as ancestral, and the timing of shifts to alternative conditions. They reveal that Early Miocene land surfaces of the CFR were wetter than at present and were dominated by quartzitic substrata. These conditions continue to characterize the higher-elevation settings of the Cape Fold Belt, where they have fostered the persistence of ancient fynbos lineages. The Middle Miocene (13–17 Ma) saw the development of perennial to weakly-seasonal arid conditions, with the strongly seasonal rainfall regime of the west coast arising ~6.5–8 Ma. Although the Late Miocene may have seen some exposure of the underlying shale substrata, the present-day substrate diversity of the CFR lowlands was shaped by Pliocene-Pleistocene events. Particularly important was renewed erosion, following the post-African II uplift episode, and the reworking of sediments on the coastal platform as a consequence of marine transgressions and tectonic uplift. These changes facilitated adaptive radiations in some, but not all, lineages studied.     

Population demography influences climatic niche evolution: evidence from diploid American Hordeum species (Poaceae)

In this study, we explore the interplay of population demography with the evolution of ecological niches during or after speciation in Hordeum. While large populations maintain a high level of standing genetic diversity, gene flow and recombination buffers against fast alterations in ecological adaptation. Small populations harbour lower allele diversity but can more easily shift to new niches if they initially survive under changed conditions. Thus, large populations should be more conservative regarding niche changes in comparison to small populations. We used environmental niche modelling together with phylogenetic, phylogeographic and population genetic analyses to infer the correlation of population demography with changes in ecological niche dimensions in 12 diploid Hordeum species from the New World, forming four monophyletic groups. Our analyses found both shifts and conservatism in distinct niche dimensions within and among clades. Speciation due to vicariance resulted in three species with no pronounced climate niche differences, while species originating due to long‐distance dispersals or otherwise encountering genetic bottlenecks mostly revealed climate niche shifts. Niche convergence among clades indicates a niche‐filling pattern during the last 2 million years in South American Hordeum. We provide evidence that species, which did not encounter population reductions mainly showed ecoclimatic niche conservatism, while major niche shifts occurred in species which have undergone population bottlenecks. Our data allow the conclusion that population demography influences adaptation and niche shifts or conservatism in South American Hordeum species.     

Climate and the evolution of annual/perennial life-histories in Nemesia (Scrophulariaceae)

The Cape Floristic Region and the Succulent Karoo in southwestern Africa are both noted for their plant species richness and high levels of endemism. The southwestern tip of Africa is one of the world's five Mediterranean-type climate regions. The biodiversity in the Cape Floristic Region and Succulent Karoo is thought to be at least partly due to changes to the climate of these regions that have occurred since the middle Miocene. Annual species are usually a significant proportion of local flora in Mediterranean-type climate regions. Previous studies of species radiations in the Cape Floristic Region have concentrated on genera that predominantly contain perennial species. Nemesia (Scrophulariaceae) comprises c. 65 species of annual and perennial herbs and sub-shrubs that are native to southern and tropical Africa. Annuals make up a significant proportion (~75%) of Nemesia species. We have reconstructed a phylogeny of 23 Nemesia species using nucleotide sequences of the ITS, ETS and trnL-spacer regions. Species were grouped into five clades, two composed of annual species, one that contained two annual and one perennial species, one that contained one annual and two perennial species, and one that was predominantly composed of perennial species. Phylogenetic dating of the ITS + ETS based phylogenetic tree using penalised likelihood suggested the genus evolved during the Miocene, and that the majority of extant Nemesia species studied radiated during the Pliocene. Ancestral state reconstruction supports at least three separate origins of the annual habit from plants with a perennial life history. One origin can be traced to the late Miocene while the other two transitions occurred more recently during the Pliocene. The transition from perennial to annual life-histories in Nemesia may have been a response to climate change.     

The Boschberg (Somerset East, Eastern Cape) — A floristic cross-roads of the southern Great Escarpment

The Boschberg and Groot-Bruintjieshoogde form the wettest and floristically most distinct section of the Sneeuberg mountain complex. As such they warrant a separate detailed investigation, particularly in terms of their connectivity between the main Sneeuberg in the west, the Great Winterberg-Amatolas in the east, and with the Cape Floristic Region (CFR) to the south and south-west. Following a detailed botanical investigation and overview we conclude that the Boschberg and Groot-Bruintjieshoogde are a floristic hub between the CFR and southern Great Escarpment, as well as between the moister eastern and drier western components of the Great Escarpment. Our data confirm that the Boschberg forms part of the south-eastern connection between the CFR and the Afromontane region in southern Africa, a connection first suggested by Weimarck (1941).     

South African Papilionoid Legumes Are Nodulated by Diverse Burkholderia with Unique Nodulation and Nitrogen-Fixation Loci

The root-nodule bacteria of legumes endemic to the Cape Floristic Region are largely understudied, even though recent reports suggest the occurrence of nodulating Burkholderia species unique to the region. In this study, we considered the diversity and evolution of nodulating Burkholderia associated with the endemic papilionoid tribes Hypocalypteae and Podalyrieae. We identified distinct groups from verified rhizobial isolates by phylogenetic analyses of the 16S rRNA and recA housekeeping gene regions. In order to gain insight into the evolution of the nodulation and diazotrophy of these rhizobia we analysed the genes encoding NifH and NodA. The majority of these 69 isolates appeared to be unique, potentially representing novel species. Evidence of horizontal gene transfer determining the symbiotic ability of these Cape Floristic Region isolates indicate evolutionary origins distinct from those of nodulating Burkholderia from elsewhere in the world. Overall, our findings suggest that Burkholderia species associated with fynbos legumes are highly diverse and their symbiotic abilities have unique ancestries. It is therefore possible that the evolution of these bacteria is closely linked to the diversification and establishment of legumes characteristic of the Cape Floristic Region.     

Patterns of weed invasion: evidence from the spatial genetic structure of Raphanus raphanistrum

Knowledge of the pathways of colonization is critical for risk assessment and management of weeds. In this study we adopted a landscape genetics approach to assess the impact of human disturbances and large-scale environmental features on the colonization of a global agricultural weed, Raphanus raphanistrum. We used nuclear microsatellite and chloroplast DNA sequence data to quantify the pattern of genetic diversity in 336 plants collected from 13 sites throughout the Cape Floristic Region, South Africa, one of the world’s recognized global biodiversity hotspots. The lack of strong spatial genetic structure suggests that R. raphanistrum colonized throughout the Cape Floristic Region via both local diffusive spread and long-distance jump dispersal. Furthermore, 47 % of analyzed plants contained Raphanus sativus (cultivated radish) chloroplast genomes, indicating historical and/or contemporary gene flow between wild and cultivated radish populations. The prevalence of high genetic diversity and long-distance gene flow are discussed in the context of ecological risk assessment.     

Intraspecific structure within three caviar-producing sturgeons (Acipenser gueldenstaedtii, A. stellatus, and Huso huso) based on mitochondrial DNA analysis

A survey of three mitochondrial DNA regions (control region, NADH5, cytochrome b) and comprehensive sequencing of the control region (631–646 bps) was conducted to examine whether subspecies and geographic populations within three species of Eurasian sturgeons, Acipenser gueldenstaedtii, A. stellatus, and Huso huso, are genetically distinct. Neither subspecies nor populations exhibited diagnostic distinction or reciprocal monophyly in any gene region examined. For the control region, molecular variance analyses (amova ) indicate that most of the variance is because of differences among haplotypes within subspecies (H. huso: 99.6%; A. stellatus: 95.0%; A. gueldenstaedtii: 81.0%) and populations (A. gueldenstaedtii: 76.1%). Significant pairwise F‐values were found for all pairwise comparisons except for Sea of Azov and Caspian Sea A. gueldenstaedtii and Caspian Sea and Black Sea A. stellatus and H. huso. Only weak genetic differentiation is apparent between select subspecies and populations, reflective of biogeographic and management history. High genetic diversity within A. gueldenstaedtii suggests the possibility of additional population structure. Future research and management projects should consider these results.