Landaeta, M. F. | Search bioRxiv

bioRxiv2024

Otolith shape variability of labrid fish from Rapa Nui (Easter Island), southeastern Pacific

Fish otolith shape provides valuable insights into the taxonomic, phylogenetic, and ecological traits of fish species. This study aimed to assess and compare the phenotypic variation in otolith shape among four labrid species (Anampses femininus, Coris debueni, Pseudolabrus fuentesi and Thalassoma lutescens) inhabiting Rapa Nui (Easter Island) in the southeastern Pacific Ocean, utilizing geometric morphometrics and aging methods. Age estimation based on otolith structure indicated that collected specimens were adults, ranging between 1 and 3 years old. Allometric analysis revealed low but significant variation (5.40%), primarily driven by changes in otolith width, resulting in distinct morphologies. Principal Component Analysis (PCA) of sagittal otoliths elucidated significant morphospace variation among species, with the first two PCs explaining 60.3% of the total variance. PC1 distinguished between elongated sagittal shapes (e.g., P. fuentesi) and robust sagittae (e.g., T. lutescens), while PC2 correlated with otolith roundness, delineating variations within species. Canonical variate analysis further highlighted differences in otolith shape, with significant variations detected among all species. The Discriminant function analysis showed high levels of discrimination accuracy for most of species pairs. Except for C. debueni-P. fuentesi (89%) and C. debueni-T. lutescens (96%), all other species pairs achieved 100% discrimination, highlighting the reliability of otolith shape as a distinguishing characteristic for the studied species. Overall, our findings emphasize the value of otolith shape analysis for characterizing and distinguishing Rapa Nui labrid species. This offers potential applications such as identifying prey within the digestive systems of large fish or bird predators in the vicinity of this isolated island in the South Pacific Ocean or archaeofauna studies.

zoology↗

bioRxiv2021

DNA reconciles morphology and colouration in the drunk blenny genus Scartichthys (Teleostei: Blenniidae) and provides insights into their evolutionary history

The blenniids of the genus Scartichthys are one of the most common fishes of Central and South American Pacific coastal reefs. This being said, Scartichthys spp. remain difficult to identify in the field, and identification is particularly challenging across the ca. 6000 km where three of the four currently accepted species are known to occur in sympatry. A reason for this is that the main taxonomic characters from traditional taxonomy are indeed elusive. Additionally, At the same time, species can display multiple colour patterns in the field, depending on their ontogenetic stage, habitat association, and reproductive behaviour. Overall, molecular characterization is warranted to help address these issues. Here, we have used a novel approach to revise the genus by combining colouration, morphological, and molecular data of representative specimens of the four currently valid species and seven described colour patterns. From this, we show that only three of the four species should be considered as valid; Scartichthys gigas (Steindachner, 1876), S. variolatus (Valenciennes, 1836), and S. viridis (Valenciennes, 1836); while S. crapulatus Williams 1990 should be synonymized with S. viridis. In the same way, our analyses show that one of the colour patterns attributed so far only to S. gigas is characteristic of the juvenile stages of S. viridis. Our time-calibrated phylogeny shows that this genus is relatively young and that the estimated time of divergence between Scartichthys gigas and S. viridis is around 1.71 Ma. In comparison, the Desventuradas and Juan Fernandez Islands endemic S. variolatus diverged about 1.95 Ma. Our results help to clarify the taxonomy of Scartichthys. SIGNIFICANCE STATEMENTThe blenniids of the genus Scartichthys are one of the most common fishes of Central and South American Pacific coastal reefs. Here we provide an updated phylogeny of this genus, comparing for the first time morphological, coloration, and molecular data in combination to resolve a 30-year-old discord among ecologists and taxonomists and discuss the potential underlying evolutionary processes that led to their presentday distribution.

zoology↗