Body-size and growth-rate divergence among populations of threespine stickleback (Gasterosteus aculeatus) in Cook Inlet, Alaska, USA

Abstract

Body size is one of the most perceptible traits of organisms and is an important fitness proxy in evolutionary studies. Oceanic threespine stickleback (Gasterosteus aculeatus L., 1758) have colonized and adapted to numerous freshwater habitats throughout the Holarctic since the most recent glacial retreat, giving us natural “replicates” of both convergent and divergent evolution. I observed considerable body-size variation among 22 threespine stickleback populations within a small region surrounding Cook Inlet, Alaska, USA. Larger bodied populations tended to have bimodal size-frequency distributions, whereas most smaller bodied populations had unimodal distributions. Bimodal distributions suggested the presence of at least two age classes within large-bodied populations. I used a Bayesian approach to infer mean size of presumed age-1 and age-2+ fish from bimodal size-frequency distributions; I found significant differences in size among populations within ages and sexes, suggesting significant divergence in growth rate among populations. I did not find significant correlations between growth rates (age-specific size) and geographic distances among populations, drainage affiliation, or distance to the sea. Thus, historical processes like isolation by distance, gene flow, or recent common ancestry did not explain differences in growth among populations, suggesting a role for local adaptation or phenotypic plasticity in size divergence.

High density, early maturing, and morphometrically unique Hippocampus erectus population makes a Bahamian pond a priority site for conservation

“…Smaller body size in this lake population cannot be completely considered dwarfism or nanism because seahorses' heads appear to have remained large, with the allometric relationship shifted between the head, body and tail. Across island and insular population examples, dwarfism is associated with a range of selective pressures, including low pH, high predator densities, the presence of larger competitors, and low food availability (Lomolino 2005, Herczeg et al 2009, MacColl et al 2013, Rollins 2017. This system displayed low predator densities in the early 1980s, but with the consistent addition of young grouper and snapper by the local fishing community since that time, and limited harvesting of crabs, it is possible that predation shifted body sizes downward.…”

Genetic structure and historic demography of endangered unarmoured threespine stickleback at southern latitudes signals a potential new management approach

“…We used bootstrap replicates ( n = 100) to estimate the variance around the estimates of IICR. We also explored results using two different mutation rates, 3.7 × 10 −8 and 6.6 × 10 −8 (Liu et al, 2016 ), and generation times of 1 and 2 years (Liu et al, 2016 ; Rollins, 2017 ), as neither parameter is known with certainty for populations in southern California or whether they differ between inland and coastal localities due to environmental heterogeneity (e.g., higher summer temperatures and greater UV exposure at inland sites). These parameters convert the values calculated by the model to estimates of time and population size.…”

Allometric relationships in morphological traits associated with foraging, swimming ability, and predator defense reveal adaptations toward brackish and freshwater environments in the threespine stickleback

“…We measured fork length to the nearest mm in the laboratory and discarded fish under 4 cm as all bony plates might not be fully developed until the fish reaches this size (Bell, 1981). Also, as the fish in this study were not aged, discarding individuals under 4 cm should leave only fish that was older than 1 year of age (Rollins, 2017;Wootton, 1976). All fish were stained in alizarin red using the modified protocol after Dingerkus and Uhler (1977), and all the lateral plates were counted directly on both sides and classified to morph according to Wootton F I G U R E 1 Study area and stickleback morphs.…”