Fig 1.
Hemolymph osmoregulatory capability in six Uca species.
Species are color-coded by population ordered on habitat salinity, after 5-days direct transfer from collecting site water to each different salinity. Populations of each species were collected from dilute (blue) to concentrated (red) media. Data (in mOsm/kg H2O) represent single measurements from single individuals in each population (8 ≤ N ≤ 51) and are adjusted to a third degree polynomial equation (0.61 ≤ R2 ≤ 0.84). 1 ‰ S = 30 mOsm/kg H2O.
Fig 2.
Hemolymph osmoregulatory capability in four Uca species.
Species are color-coded by population ordered on habitat salinity, after 5-days direct transfer from collecting site water to each different salinity. Populations of each species were collected from dilute (blue) to concentrated (red) media. Data (in mOsm/kg H2O) represent single measurements from single individuals in each population (12 ≤ N ≤ 57) and are adjusted to a third degree polynomial equation (0.75 ≤ R2 ≤ 0.85). 1 ‰ S = 30 mOsm/kg H2O.
Table 1.
Osmoregulatory traits for all Uca species evaluated to date from the American and Indo-west Pacific regions.
We provide habitat and hemolymph osmolalities, lower (LL50) and upper (UL50) lethal limits, hemolymph osmolalities at LL50 (OsmLL50) and UL50 (OsmUL50), and isosmotic point (all in mOsm/kg H2O; 30 mOsm/kg H2O = 1 ‰ salinity), and calculated indices of hyper- and hypo-regulatory buffering capabilities. Indices close to 1 reflect substantial ability to buffer hemolymph osmolality against variation in external osmolality; values near 0 reveal very limited regulatory ability, reflecting restricted ability to maintain hemolymph osmolality. Species are ordered on increasing habitat salinity within each region.
Fig 3.
Phylogenetic correlogram showing Moran’s I coefficients for 9 osmoregulatory traits at 4 distance classes in the Uca phylogeny modified from Shih et al. (2015).
Horizontal line at I = 0.0 indicates the expected value under the null hypothesis of no autocorrelation. Habitat and hemolymph osmolalities, isosmotic concentration and hyper-osmoregulatory index (RCHyper) showed positive autocorrelation for the first and second distance classes, shifting to either negative or no autocorrelation for the other two classes, demonstrating strong phylogenetic structuring. However, traits associated with the lower (LL50) and upper (UL50) lethal limits, and their respective hemolymph osmolalities (OsmLL50, OsmUL50) and with hypo-osmoregulatory capacity (RCHypo) do not correlate significantly with phylogeny for any distance class.
Fig 4.
Estimation of ancestral states by maximum likelihood analysis for habitat osmolality (mOsm/kg H2O, left panel, 1 ‰ salinity = 30 mOsm/kg H2O) and hemolymph osmolality (mOsm/kg H2O, right panel) in the fiddler crab topology modified from Shih et al. (2015).
Both traits are positively associated (PGLS slope = 0.30, F = 43.8, P < 0.001, α = 2.1) suggesting correlated evolution. A, B, C and D are natural groupings particularly relevant to the interpretation of osmoregulatory evolution [A, genus Uca; B and C, American clades; D, Indo-west Pacific clade].
Fig 5.
Estimation of ancestral states by maximum likelihood analysis for hyper- and hypo-osmoregulatory indices (left and right panels, respectively) in the fiddler crab topology modified from Shih et al. (2015).
Indices close to 1 reflect substantial ability to regulate hemolymph osmolality against variation in external osmolality; values near 0 reveal very limited regulatory ability, reflecting restricted capability to maintain hemolymph osmolality. The evolution of the two indices is not correlated (PGLS slope = 0.11, F = 1.7, P < 0.81, α = 0.6), and neither index is linked to habitat osmolality (PGLS slope ≈0.0, 0.8 ≤ F ≤ 3.3, 0.1 ≤ P ≤ 0.4, 0.3 ≤ α ≤ 1.7). However, an association between the indices is revealed at more inclusive levels. A, B, C and D are natural groupings particularly relevant to the interpretation of osmoregulatory evolution [A, genus Uca; B and C, American clades; D, Indo-west Pacific clade].
Fig 6.
Evolutionary history of shifts in adaptive peaks of Uca osmoregulatory ability mapped onto the fiddler crab topology modified from Shih et al. (2015).
Each color represents an optimum for all 9 osmoregulatory traits (see Table 1) analyzed together using SURFACE. The first peak (blue) was detected at the tree root and is shared by the American clades, i. e., the subgenera Uca, Minuca and Leptuca. A second peak (red) occurs in the Indo-west Pacific species, with a shift in U. inversa (black), the last optimum.
Fig 7.
Results of a SURFACE analysis using osmoregulatory traits in 24 Uca species.
A, Relative contribution of osmoregulatory traits in Uca to model fitting, showing the Partial AIC scores for each (colored lines), and for all traits together (multidimensional) (black line). Hyper- (RChyper) and hypo- (RChypo) osmoregulatory indices contributed strongly to model fitting by reducing the AIC values. Hemolymph osmolality, osmolality at LL50, and isosmotic concentration contributed moderately to the model; all other osmoregulatory traits reduced model fitting. B, C and D, Estimated position of the species’ traits and adaptive peaks, considering only those traits whose correlations were tested. Large filled circles represent the three optima. Small filled circles are the trait values for each of the 24 fiddler crab species evaluated, colored according to the adaptive peak to which they belong.