Variation in surfperch diets between allopatry and sympatry: circumstantial evidence for competition

Advances and Limitations of Next Generation Sequencing in Animal Diet Analysis

Diet analysis is a critical content of animal ecology and the diet analysis methods have been constantly improving and updating. Contrary to traditional methods of high labor intensity and low resolution, the next generation sequencing (NGS) approach has been suggested as a promising tool for dietary studies, which greatly improves the efficiency and broadens the application range. Here we present a framework of adopting NGS and DNA metabarcoding into diet analysis, and discuss the application in aspects of prey taxa composition and structure, intra-specific and inter-specific trophic links, and the effects of animal feeding on environmental changes. Yet, the generation of NGS-based diet data and subsequent analyses and interpretations are still challenging with several factors, making it possible still not as widely used as might be expected. We suggest that NGS-based diet methods must be furthered, analytical pipelines should be developed. More application perspectives, including nutrient geometry, metagenomics and nutrigenomics, need to be incorporated to encourage more ecologists to infer novel insights on they work.

Trophic resource partitioning drives fine-scale coexistence in cryptic bat species

Understanding the processes that enable species coexistence has important implications for assessing how ecological systems will respond to global change. Morphology and functional similarity increase the potential for competition, and therefore, co-occurring morphologically similar but genetically unique species are a good model system for testing coexistence mechanisms. We used DNA metabarcoding and high-throughput sequencing to characterize for the first time the trophic ecology of two recently described cryptic bat species with parapatric ranges, Myotis escalerai and Myotis crypticus. We collected fecal samples from allopatric and sympatric regions and from syntopic and allotopic locations within the sympatric region to describe the diets both taxonomically and functionally and compare prey consumption with prey availability. The two bat species had highly similar diets characterized by high arthropod diversity, particularly Lepidoptera, Diptera and Araneae, and a high proportion of prey that is not volant at night, which points to extensive use of gleaning. Diet overlap at the prey item level was lower in syntopic populations, supporting trophic shift under fine-scale co-occurrence. Furthermore, the diet of M. escalerai had a marginally lower proportion of not nocturnally volant prey in syntopic populations, suggesting that the shift in diet may be driven by a change in foraging mode. Our findings suggest that fine-scale coexistence mechanisms can have implications for maintaining broad-scale diversity patterns. This study highlights the importance of including both allopatric and sympatric populations and choosing meaningful spatial scales for detecting ecological patterns. We conclude that a combination of high taxonomic resolution with a functional approach helps identify patterns of niche shift.

A peacock bass (Cichla) functional novelty relaxes a constraint imposed by the classic cichlid pharyngeal jaw innovation

Innovations may provide access to new resources but often result in significant trade-offs. Pharyngognathy is a classic pharyngeal jaw innovation in which the left and right lower pharyngeal jaw (LPJ) bones are united into a single structure, producing a strong bite but reduced gape. Throughout cichlids, pharyngeal suturing occurs along the entire medial border between LPJ bones, except in peacock bass (Cichla), where these bones are connected by ligaments only in their anterior region. We show that this limited attachment permits the jaw bones to spread apart and we link this feature to an increase in pharyngeal gape that is comparable to non-pharyngognathous species. The capacity of the LPJ bones to spread apart is strongest in juveniles and is mostly lost during development. Juvenile Cichla exhibit size-specific pharyngeal gape similar to non-pharyngognathous percomorphs; however, adults exhibit pharyngeal gape on par with other predatory cichlids. Relaxation of pharyngeal suturing offsets a major deleterious consequence of pharyngognathy by reducing gape limitation and we propose this may accelerate the ontogenetic transition to piscivory. Partial reversal of the classic cichlid pharyngeal jaw innovation highlights the functional trade-offs that often accompany innovations and may be a major cause of variation in their macroevolutionary consequences.

Shoaling preference and evidence for maintenance of sibling groups by juvenile black perch Embiotoca jacksoni

Group sizes in free-living juvenile black perch Embiotoca jacksoni were quantified and predictions of the hypothesis that such groups comprise sibling brood-mates were tested. Group sizes in the field were within the range of female brood sizes and often occurred close to each other but did not merge. In captivity, juveniles formed groups immediately after birth. In laboratory experiments, they also associated significantly more with chambers containing familiar members of their own brood than empty chambers but did not associate more with chambers containing similar-sized juveniles from a different brood. Juvenile E. jacksoni also associated significantly more with chambers containing familiar brood-mates than with chambers containing unfamiliar members of a different brood. The strength of this preference increased with the number of days fish had been together since birth. When two broods were placed in a large outdoor tank, all individuals from both broods directed significantly more aggressive acts towards members of the other brood than towards members of their own brood. While the relative effects of familiarity and relatedness cannot be completely separated in this viviparous species, associating with familiar individuals would facilitate the maintenance of sibling groups in the field.