Ecological and landscape effects on genetic distance in an assemblage of headwater fishes

Abstract

Environmental divergence along hierarchically structured longitudinal gradients may constitute barriers to gene flow in river networks for headwater specialised species.While known, this phenomenon has not been well studied, especially with regard to degree of headwater specialisation. We examined six headwater species that differ in habitat specialisation to assess whether patterns of differentiation vary according to geographic or environmental distance. We also identified regional environmental or anthropogenically induced fragmentation effects by comparing within-drainage patterns of genetic distance across replicate watersheds. We used a comparative modelling framework to determine whether isolation by distance or isolation by resistance of large river habitats was a better predictor of genetic distance across species. The influence of reservoir presence and regional network characteristics that may influence the hydrology and size of large river habitats were also assessed. Resistance effects from large rivers were closely related to headwater specialisation, with increased specialisation leading to increased resistance and loss of drainagewide population connectivity. These results affirm that dendritic networks naturally fragment headwater specialised species. Further isolation from anthropogenic fragmentation was detected in two of the six drainages, indicating interactions with system-specific conditions. Landscape variables related to the hydrology of large rivers also affected genetic distance in predicted ways, supporting the importance of large rivers in genetically structuring headwater species in drainage networks. K E Y W O R D Sisolation by distance, isolation by resistance, landscape genetics, niche breadth, reservoir, riverscape genetics

Fish dispersal in flowing waters: A synthesis of movement‐ and genetic‐based studies

“…Nonetheless, prioritizing and making effective conservation plans require complementary information on both demographic and genetic aspects of population status (Paz‐Vinas et al., ). As such, genetic‐based approaches provide a powerful way to identify fine‐scale population structure and to shed light on the processes shaping patterns of genetic diversity and functional connectivity, both of which are central concern to conservation and management (McRae & Beier, ; Schmidt & Schaefer, ).…”

Hydrographic correlates of within‐river distribution and population genetic structure in two widespread species of mountain galaxias (Teleostei, Galaxiidae) in southern Australia

“…Stream and valley slope were significantly correlated with spatial genetic variation in G. olidus, as shown for other species with headwater distributions (e.g. Cook et al, 2011;Hughes et al, 2013;Schmidt & Schaefer, 2017), and even in some fishes with relatively low elevation distributions (Faulks et al, 2011). There were no statistically significant relationships between spatial genetic variation and any hydrographic factor for G. oliros because only four populations were available (i.e.…”

“…This suggests that hydrographic factors associated with upper catchment areas (e.g. steep stream slopes) may isolate populations of G. olidus (see Cook, Kennard, Real, Pusey, & Hughes, ; Fagan, ; Faulks, Gilligan, & Behereharay, ; Hughes, Huey, & Schmidt, ; Schmidt & Schaefer, ), whereas populations of G. oliros in lowland and foothill stream segments are likely to have greater magnitudes of connectivity (see Gyllensten, ).…”

Modelling patterns of coexistence of three congeneric headwater fishes

“…Many headwater fishes exhibit dispersal patterns that adhere to the stream hierarchy model (Meffe & Vrijenhoek, 1988) predicting that hierarchically nested drainages are more likely to exchange organisms. Ecological trait selection within headwater streams is a result of the isolation of unique habitats across a river system (Mundahl & Ingersoll, 1983;Petty & Grossman, 2004;Schmidt & Schaefer, 2018). Morphological adaptations to these unique habitat patches such as small body size and caudal fin shape, both of which affect swimming performance, may further limit dispersal of headwater specialists (Hudy & Shiflet, 2009;Ovidio, Detaille, Bontinck, & Philippart, 2009;Petty & Grossman, 2004).…”