Low Genetic Diversity and Complex Population Structure in Black Piranha (Serrasalmus rhombeus), a Key Amazonian Predator

The black piranha (Serrasalmus rhombeus), a widely spread species in the rivers of the Amazon basin, plays a vital role as both key predator and important prey. Despite its essential contribution to ecosystem stability, there is a lack of information regarding its genetic diversity and population dynamics in the central Amazon region. As the Amazon continues to undergo environmental changes in the context of growing anthropogenic threats, such knowledge is fundamental for assist in the conservation of this species. This study is the first to analyze the genetic diversity and population structure of S. rhombeus in the central Amazon region using high-resolution genomic data. We employed a Genotyping-by-Sequencing approach with 248 samples across 14 study sites from various tributaries, encompassing diverse water types (black, white, and clear water) and characterized by 34 physiochemical parameters. The data reveals low diversity accompanied by pronounced signs of inbreeding in half of the sites and robust genetic differentiation and variation among sites and within-sites. Surprisingly, we also found evidence of higher dispersal capacity than previously recognized. Our analysis exposed a complex and high population structure with genetic groups exclusive to some sites. Gene flow was low and some groups presented ambiguous genealogical divergence index (gdi) signals, suggesting the occurrence of potential cryptic species. Moreover, our results suggest that the population structure of black piranha appears more influenced by historical events than contemporary factors. These results underscore the need to give greater attention to this keystone species, for which no regulatory framework or conservation strategies is presently in effect.

Selected Wildlife Trematodes

The trematodes are a species-rich group of parasites, with some estimates suggesting that there are more than 24,000 species. However, the complexities associated with their taxonomic status and nomenclature can hinder explorations of the biology of wildlife trematodes, including fundamental aspects such as host use, life cycle variation, pathology, and disease. In this chapter, we review work on selected trematodes of amphibians, birds, mammals, and their snail intermediate hosts, with the goal of providing a tool kit on how to study trematodes of wildlife. We provide a brief introduction to each group of wildlife trematodes, followed by some examples of the challenges each group of trematodes has relative to the goal of their identification and understanding of the biology and interactions these organisms have with their wildlife hosts.

How we study cryptic species and their biological implications: A case study from marine shelled gastropods

Methodological and biological considerations are intertwined when studying cryptic species. A potentially large component of modern biodiversity, the frequency of cryptic species among taxonomic groups is not well documented. The term "cryptic species" is imprecisely used in scientific literature, causing ambiguity when interpreting their evolutionary and ecological significance. This study reviews how cryptic species have been defined, discussing implications for taxonomy and biology, and explores these implications with a case study based on recently published literature on extant shelled marine gastropods. Reviewed gastropods were recorded by species. Records of cryptic gastropods were presented by authors with variable levels of confidence but were difficult to disentangle from inherent biases in the study effort. These complexities notwithstanding, most gastropod species discussed were not cryptic. To the degree that this review's sample represents extinct taxa, the results suggest that a high proportion of shelled marine gastropod species are identifiable for study in the fossil record. Much additional work is needed to provide a more adequate understanding of the relative frequency of cryptic species in shelled marine gastropods, which should start with more explicit definitions and targeted case studies.

Evaluating the taxonomic status of the large sized Tricolia Risso, 1826 in the Northeast Atlantic and Mediterranean Sea

Despite a long history of taxonomic studies on the genus Tricolia Risso, 1826, there is a shortfall on thorough systematic molecular reviews of the taxon from the NE Atlantic and Mediterranean coasts. Aiming to assess the genetic distinctness among morphospecies and the taxonomic status of currently accepted large sized species in these areas, we conducted a molecular phylogenetic analysis of the genus based on one mitochondrial (cox1) and two nuclear (28S and ITS2) markers. Seven Tricolia species were consistently retrieved in the analyses, including a new genetic lineage in the NE Atlantic designated as Tricolia sp. 1. Molecular analyses revealed that only one species, T. azorica, occurs in the NE Atlantic archipelagos. The sister taxa T. pullus (Mediterranean) and T. picta (NE Atlantic) should be classified as distinct species, instead of subspecies of the T. pullus group (sensu Gofas 1982). Tricolia miniata is also a complex of species in the Mediterranean and future studies across the distribution range are necessary to clarify its status.