Shared and unique patterns of phenotypic diversification along a stream gradient in two congeneric species

Abstract

Stream ecosystems show gradual variation of various selection factors, which can result in a zonation of species distributions and gradient evolution of morphological and life-history traits within species. Identifying the selective agents underlying such phenotypic evolution is challenging as different species could show shared and/or unique (species-specific) responses to components of the river gradient. We studied a stream gradient inhabited by two mosquitofishes (genus Gambusia) in the Río Grijalva basin in southern Mexico and found a patchy distribution pattern of both congeners along a stretch of 100 km, whereby one species was usually dominant at a given site. We uncovered both shared and unique patterns of diversification: some components of the stream gradient, including differences in piscine predation pressure, drove shared patterns of phenotypic divergence, especially in females. Other components of the gradient, particularly abiotic factors (max. annual temperature and temperature range) resulted in unique patterns of divergence, especially in males. Our study highlights the complexity of selective regimes in stream ecosystems. It exemplifies that even closely related, congeneric species can respond in unique ways to the same components of the river gradient and shows how both sexes can exhibit quite different patterns of divergence in multivariate phenotypic character suites.

Thermal regime drives a latitudinal gradient in morphology and life history in a livebearing fish

“…In essence, fish from higher latitudes had body morphologies that reflected/facilitated increased investment into reproduction and a tendency to produce larger clutch sizes. In environments where selection favours r-selected life-history strategies, indirect selection probably favours a body shape that increases body cavity space to house the larger testes (for males) and larger clutches (for females; for a similar pattern in G. sexradiata and G. yucatana see Jourdan et al, 2016). Our observed patterns are consistent with this: first, males in northern latitudes tended to exhibit ventral deepening of the body (d 3 ; OSM Fig.…”

“…In this way, we minimized confounding environmental factors known to influence phenotypic variation in some livebearing fishes (e.g. Alcaraz & Garcia-Berthou, 2007;Carmona-Catot et al, 2011;Jourdan et al, 2016), permitting us to focus more directly on environmental factors of interest in this study. We collected G. holbrooki using a combination of seine (4 m long, 3-mm mesh-width) and dip nets (1.6-mm mesh-width).…”

Molecular evolution and expression of oxygen transport genes in livebearing fishes (Poeciliidae) from hydrogen sulfide rich springs

“…The only groups with moderately supported relationships included the two populations of G. sexradiata and G. eurystoma (bootstrap support 60%, Fig. 1), which have previously been found to represent a complex of closely related and recently diverged species (Jourdan et al 2016).…”

Distribution, Spread, and Habitat Predictability of a Small, Invasive, Piscivorous Fish in an Important Estuarine Fish Nursery

“…In freshwater habitat of south Florida's Everglades National Park, Kerfoot et al [37] found a positive relationship between pH (range:~7.4-8.0) and B. belizanus density at one site, a weak positive relationship at another site (pH range:~7.2-7.4), and negative relationships at two other sites (pH ranges:~7.3-7.6 and~7.6-8.1). Multispecies ordination analyses within the native range do not demonstrate strong or consistent relationships between pH and B. belizanus populations [33][34][35][36]. As noted by Kerfoot et al [37], changes in pH are known to directly affect ion uptake across gills and internal acid-base balance in fishes, ultimately affecting survival rates.…”