Patterns of genetic structuring at the northern limits of the Australian smelt (Retropinna semoni) cryptic species complex

Abstract

Freshwater fishes often exhibit high genetic population structure due to the prevalence of dispersal barriers (e.g., waterfalls) whereas population structure in diadromous fishes tends to be weaker and driven by natal homing behaviour and/or isolation by distance. The Australian smelt (Retropinnidae: Retropinna semoni) is a native fish with a broad distribution spanning inland and coastal drainages of south-eastern Australia. Previous studies have demonstrated variability in population genetic structure and movement behaviour (potamodromy, facultative diadromy, estuarine residence) across the southern part of its geographic range. Some of this variability may be explained by the existence of multiple cryptic species. Here, we examined genetic structure of populations towards the northern extent of the species’ distribution, using ten microsatellite loci and sequences of the mitochondrial cyt b gene. We tested the hypothesis that genetic connectivity among rivers should be low due to a lack of dispersal via the marine environment, but high within rivers due to dispersal. We investigated populations corresponding with two putative cryptic species, SEQ-North (SEQ-N), and SEQ-South (SEQ-S) lineages occurring in south east Queensland drainages. These two groups formed monophyletic clades in the mtDNA gene tree and among river phylogeographic structure was also evident within each clade. In agreement with our hypothesis, highly significant overall FST values suggested that both groups exhibit very low dispersal among rivers (SEQ-S FST = 0.13; SEQ-N FST= 0.27). Microsatellite data indicated that connectivity among sites within rivers was also limited, suggesting dispersal may not homogenise populations at the within-river scale. Northern groups in the Australian smelt cryptic species complex exhibit comparatively higher among-river population structure and smaller geographic ranges than southern groups. These properties make northern Australian smelt populations potentially susceptible to future conservation threats, and we define eight genetically distinct management units along south east Queensland to guide future conservation management. The present findings at least can assist managers to plan for effective conservation and management of different fish species along coastal drainages of south east Queensland, Australia.

Non‐diadromous life history and limited movement in northern lineages of Australian smelt: Evidence from otolith chemistry analysis

“…Consistent with this prediction, a microsatellite study of the same populations as reported on here, showed very high levels of genetic differentiation (Islam, Schmidt, Crook, & Hughes, 2018) for both lineages.…”

“…If dispersal was strongly limited for extended periods, some genetic differentiation would be expected due to the effects of genetic drift, different selection pressure or both. However, no significant pairwise F ST values between upstream and downstream sites of two of those three rivers (Logan and Nerang River) with low variation within Brisbane River were reported from genetic analysis of these same sites (Islam et al, 2018),…”

Improved genetic markers for monitoring recruitment dynamics in the endangered Mary River cod (Maccullochella mariensis)

“…In particular we've demonstrated the util- catchments. These include crustaceans (Bentley, Schmidt, & Hughes, 2010;Sharma & Hughes, 2009), fishes (Bishop, Hughes, & Schmidt, 2018;Hughes et al, 2015;Islam, Schmidt, Crook, & Hughes, 2018) and a turtle endemic to the Mary River (Schmidt, Espinoza, Connell, & Hughes, 2018). Together these findings highlight the significance of Tinana Creek as an important reservoir of intraspecific diversity in Mary River cod and numerous other freshwater taxa.…”