Phenotypic and genetic variation in the white croaker Micropogonias furnieri Desmarest 1823 (Perciformes: Sciaenidae): testing the relative roles of genetic drift and natural selection on population divergence

Ocean warming favours a northern Argyrosomus species over its southern congener, whereas preliminary metabolic evidence suggests that hybridization may promote their adaptation

Anthropogenic-induced climate change is having profound impacts on aquatic ecosystems, and the resilience of fish populations will be determined by their response to these impacts. The northern Namibian coast is an ocean warming hotspot, with temperatures rising faster than the global average. The rapid warming in Namibia has had considerable impacts on marine fauna, such as the southern extension of the distribution of Argyrosomus coronus from southern Angola into northern Namibian waters, where it now overlaps and hybridizes with the closely related Namibian species, A. inodorus. Understanding how these species (and their hybrids) perform at current and future temperatures is vital to optimize adaptive management for Argyrosomus species. Intermittent flow-through respirometry was used to quantify standard and maximum metabolic rates for Argyrosomus individuals across a range of temperatures. The modelled aerobic scope (AS) of A. inodorus was notably higher at cooler temperatures (12, 15, 18 and 21°C) compared with that of A. coronus, whereas the AS was similar at 24°C. Although only five hybrids were detected and three modelled, their AS was in the upper bounds of the models at 15, 18 and 24°C. These findings suggest that the warming conditions in northern Namibia may increasingly favour A. coronus and promote the poleward movement of the leading edge of their southern distribution. In contrast, the poor aerobic performance of both species at cold temperatures (12°C) suggests that the cold water associated with the permanent Lüderitz Upwelling Cell in the south may constrain both species to central Namibia. This is most concerning for A. inodorus because it may be subjected to a considerable coastal squeeze.

Morphological diversity within the Ozark minnow (Notropis nubilus: Leuciscidae)

The Ozark minnow, Notropis nubilus, is a small stream fish that has a disjunct distribution in the Ozark Plateau and upper Mississippi River basin. Three reciprocally monophyletic and deeply divergent lineages have been hypothesized within the species based on molecular data. These lineages are allopatric and isolated from each other. The objective of this study was to test the hypothesis that these lineages and the disjunct population in the upper Mississippi River basin are morphologically distinct. Meristic and geometric morphometric data were used to identify and quantify morphological diversity within the Ozark minnow. Analyses of the meristic data and a principal component analysis of the morphometric data were unable to find any noticeable differences in morphology among groups. However, canonical variates analyses of the morphometric data and linear models were able to define statistically significant differences in shape. Analyses of all-individuals were able to identify shape differences between all groups. Males-only analyses were less conclusive, but there was some indication that males may be diverging more quickly than all-individuals. The detection of subtle variation in shape implies selection is not a strong factor in morphological divergence and observed differences are most likely due to morphological drift. This indicates that the lineages within the Ozark minnow are likely on the trajectory for speciation. The allopatric nature of these clades makes the Ozark minnow an interesting model for the study of morphological drift and speciation.

A new analysis interpreting Nilotic relationships and peopling of the Nile Valley

The process of the peopling of the Nile Valley likely shaped the population structure and early biological similarity of Egyptians and Nubians. As others have noted, affinity among Nilotic populations was due to an aggregation of events, including environmental, linguistic, and sociopolitical changes over a great deal of time. This study seeks to evaluate the relationships of Nubian and Egyptian groups in the context of the original peopling event. Cranial nonmetric traits from 18 Nubian and Egyptian samples, spanning Lower Egypt to Lower Nubia and approximately 7400 years, were analyzed using Mahalanobis D² as a measure of biological distance. A principal coordinates analysis and spatial-temporal model were applied to these data. The results reveal temporal and spatial patterning consistent with documented events in Egyptian and Nubian population history. Moreover, the Mesolithic Nubian sample clustered with later Nubian and Egyptian samples, indicating that events prior to the Mesolithic were important in shaping the later genetic patterning of the Nubian population. Later contact through the establishment of the Egyptian fort at Buhen, Kerma's position as a strategic trade center along the Nile, and Egyptian colonization at Tombos maintained genetic similarity among the populations.

Genetic and Morphological Variation of the Forkbeard, Phycis phycis (Pisces, Phycidae): Evidence of Panmixia and Recent Population Expansion along Its Distribution Area

The knowledge of population structure of a species is essential to effectively assess and manage fisheries. In the present study, genetics, by mitochondrial DNA cytochrome b sequence analysis, and body geometric morphometrics were used to evaluate the existence of distinct populations of the forkbeard (Phycis phycis), an important commercial species in several European countries, especially Portugal and Spain. For geometric morphometric analysis, specimens were collected in the Northeast Atlantic Ocean—Azores, Madeira and mainland Portugal, and for genetic analysis, these samples were complemented with samples collected in the Mediterranean Sea—Spain, Italy and Croatia, in order to cover the entire distribution area of the species. Body shape of the forkbeard from the Northeast Atlantic was found to be highly variable. This variation was probably associated with different environmental factors between the study areas. Despite morphological variation, a low genetic differentiation between samples from different areas was found, most likely due to gene flow that occurred in the past or with the demographic history of the species. Moreover, the presence of unique haplotypes in the Northeast Atlantic and in the Mediterranean suggests that recent gene flow between populations from these areas should be limited. Altogether, a high haplotype diversity, a low nucleotide diversity, a “star-like” network and the results of the mismatch distribution, indicate a possible signature of recent population expansions, which probably started during the end of the Last Glacial Maximum and led to the colonization of the Northeast Atlantic and the Mediterranean.

Contrasting patterns of morphological variation with dietary preferences in Micropogonias furnieri: insights from stable-isotope and digestive-trait analyses

The dietary preferences of populations of whitemouth croaker Micropogonias furnieri, which commonly inhabit estuarine and oceanic environments of the south-western Atlantic Ocean, were investigated using stable-isotope analysis and digestive traits, and compared with previous genetic and morphometric surveys of this species. Isotopic and C:N-derived data suggested that individuals from coastal lagoons are the most differentiated from the remaining localities surveyed. In contrast, the analysis of the digestive traits did not show the same differentiation pattern. The overall correlation between isotopic, molecular and morphological variations suggests that genetic and phenotypic differences among populations are accompanied by differential resource use, supporting the idea that selective forces could be playing an important role in population differentiation.