Environmentally Modulated Repeat Evolution of Polymorphic Arctic Charr Life History Traits

Sympatric Arctic charr, Salvelinus alpinus (L. 1758), morphs have flexible but repeated life history strategies tested across five Norwegian lakes. In several Scandinavian polymorphic Arctic charr populations differentiated by their diet and habitat use, a large littoral omnivorous (LO) morph commonly cooccurs with a smaller profundal spawning (PB/PZ) morph. A third, large piscivorous (PP) morph is also known to occur within a portion of Arctic charr populations in the profundal habitat along with the PB/PZ individuals. Life history traits, such as age at maturity, growth, and diet are known to differ among coexisting morphs. Notably, the PP morph was the longest morph with the oldest age at maturity while the PB/PZ morph showed the shortest lengths overall and youngest age with LO morph being intermediate in both traits. Growth parameters differed across all the morphs. When examining growth within morph groups, the LO morph was found to have different growth across all lakes, while similar reproductive investments and different energy acquisition patterns were seen within the PB/PZ and PP morphs. These results suggest repeat evolution in several life history strategies of reproductively isolated Arctic charr sympatric morphs, notably for the first time in the PP morph, while also highlighting the importance of the local environment in modulating life history traits.

Genetic Causes and Consequences of Sympatric Morph Divergence in Salmonidae: A Search for Mechanisms

Repeatedly and recently evolved sympatric morphs exhibiting consistent phenotypic differences provide natural experimental replicates of speciation. Because such morphs are observed frequently in Salmonidae, this clade provides a rare opportunity to uncover the genomic mechanisms underpinning speciation. Such insight is also critical for conserving salmonid diversity, the loss of which could have significant ecological and economic consequences. Our review suggests that genetic differentiation among sympatric morphs is largely nonparallel apart from a few key genes that may be critical for consistently driving morph differentiation. We discuss alternative levels of parallelism likely underlying consistent morph differentiation and identify several factors that may temper this incipient speciation between sympatric morphs, including glacial history and contemporary selective pressures. Our synthesis demonstrates that salmonids are useful for studying speciation and poses additional research questions to be answered by future study of this family. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Parallel Evolution of Allometric Trajectories of Trophic Morphology between Sympatric Morphs of Mesoamerican Astyanax (Characidae)

Parallel evolution of the body shape and trophic-related traits has been detected between sympatric pairs of lake-dwelling characin fishes in Mesoamerica. Here, we evaluated the variation in and the ontogenetic allometric trajectories of trophic morphology between sympatric Astyanax morphs (elongate and deep-body) in two geographic systems, Lake Catemaco (Mexico) and San Juan River basin (Nicaragua and Costa Rica). Using geometric morphometrics, we determined the shape variation and disparity in the premaxillary bone, and the patterns of allometric trajectories between morphs in each system. We found a higher differentiation and disparity in the premaxilla shape between morphs from San Juan River basin than between the Lake Catemaco ones. We found shared (parallel evolution) patterns of divergence between systems, which included allometric trajectories showing a positive correlation between the premaxilla shape and log centroid size, as well as trajectories being extended in the elongated-body morph (truncated in the deep-body morph). Regarding the unique patterns of divergence, we recovered parallel allometric trajectories between morphs from Lake Catemaco, while the San Juan River basin morphs showed divergent trajectories. Our results are congruent with the hypothesis that divergence in trophic morphology can be considered a triggering factor in the divergence in the genus Astyanax from Mesoamerica.

A geographical cline in craniofacial morphology across populations of Mesoamerican lake-dwelling fishes

The complex geological history and tropical climate of Mesoamerica create a rich source of biodiversity from which we can study evolutionary processes. Here, we discuss highly divergent forms of lake-dwelling fishes distributed across southern Mexico and Central America, originally recognized as members of different genera (AstyanaxandBramocharax). Recent phylogenetic studies suggest these morphotypes group within the same genus and readily hybridize. Despite genetic similarities,Bramocharaxmorphs exhibit stark differences in cranial shape and dentition. We investigated the evolution of several cranial traits that vary across morphs collected from four lakes in Mexico and Nicaragua and discovered an ecomorphological cline from the northern to southern lakes. Northern populations of sympatric morphs exhibit similar cranial shape and tooth morphology. Southern populations ofBramocharax, however, have more maxillary teeth, larger unicuspid teeth, an elongated snout and a streamlined cranium compared toAstyanax. The divergence of craniofacial morphology in southern lakes likely evolved in response to environmental pressures. We discuss the ecological differences across the four lake systems in terms of geological history and trophic dynamics. In summary, our study suggests thatBramocharaxare likely locally-adapted members derived fromAstyanaxlineages, highlighting the complex evolutionary history of theAstyanaxgenus.

In search of the real Pseudomallada prasinus (Neuroptera, Chrysopidae)

Three sympatric morphs of Pseudomallada prasinus (Burmeister, 1839) were hybridized in search of reproductively separated species. In addition, 26 morphological and biological traits were recorded for living and preserved specimens of the three morphotypes. Cross-breeding experiments showed that the prasinoid morph “marianus” is a different species from either the “greenhead” or “sulfurhead” morphs. All three are morphologically and biologically distinct. “Greenhead” and “sulfurhead” are small to medium sized and deposit eggs singly, without obligatory diapause in the second instar. In most specimens of these two smaller “prasinus” morphs there is a red or brown suture below the antennae, which can fade with age or preservation. P. “marianus” is a large species, depositing bundled eggs, with an obligatory diapause in about half of the L2. In none of the collected or reared P. “marianus” was a red or brown suture below the eyes observed. The forewing sizes of the type specimens of Chrysopa prasina Burmeister, 1839, C. coerulea Brauer, 1851, and C. marianus Navás, 1915 differ significantly from those of C. aspersa Wesmael, 1841 and other, later synonymized type specimens such as C. sachalinensis Matsumura, 1911, C. burri Navás, 1914, C. caucasica Navás, 1914, or C. vernalis Navás, 1926. This strongly suggests that the “marianus” morph is the real P. prasinus and the “greenhead” and “sulfurhead” morphs correspond to P. aspersus or one of the later synonymized species with smaller wing size.Pseudomallada marianus (Navás, 1905) is confirmed as a synonym of P. prasinus, depositing bundled eggs, whereas smaller prasinoid morphs, depositing single eggs, are not P. prasinus—and are morphologically distinct from P. abdominalis (Brauer, 1856). Pseudomallada aspersus (Wesmael, 1841) is a valid species, but at this point it is not possible to assign it to one of the prasinoid morphs because most of the live color traits are not discernible in old type specimens. A diagnostic description of the “real” P. prasinus can separate almost all P. prasinus specimens, even in museum collections, from P. aspersus (likely to be the “greenhead” morph) and the Mediterranean “sulfurhead”.