Longitudinal patterns and linkages in benthic fine particulate organic matter composition, respiration, and nutrient uptake

James M. Hood, Lyndsie M. Collis, John D. Schade, Rebecca A. Stark, Jacques C. Finlay. 2021. https://doi.org/10.1002/lno.11781

Abstract

Longitudinal changes in the structure and function of river ecosystems have long been recognized, yet our understanding of how such patterns shape elemental cycles remains limited. In particular, while benthic fine particulate organic matter (POM, 0.7–1000 μm) may control many stream nutrient cycles, less is known about longitudinal patterns or controls of benthic POM-associated nutrient uptake. We conducted a survey of benthic POM-associated respiration and nutrient uptake as well as microbial biomass (bacteria and algae) and benthic POM composition in four size classes (0.7–53 μm, 53–106 μm, 106–250 μm, and 250–1000 μm) in six streams in the forested South Fork Eel River watershed (California), encompassing a longitudinal gradient in light availability and primary production. Benthic POM at downstream sites was composed of smaller particles with lower organic matter content that were richer in nitrogen and autotrophic material. Areal respiration and nutrient uptake rates increased 11- to 67-fold with stream size. While microbial activity rates did not increase with stream size, benthic POM-associated microbial biomass increased 20-fold with stream size, and closely tracked a 15-fold increase in light availability, and primary production. Thus, microbial biomass, not activity, determined longitudinal patterns in benthic POM-associated areal nutrient uptake and respiration rates. We attribute longitudinal patterns in microbial biomass to increases in light availability and primary production. Our findings help clarify the role of local (primary production) and upstream processes in shaping ecosystem structure and function.

Alternative prey reduces Largemouth Bass predation mortality on newly stocked Channel Catfish fingerlings

Cory Becher, Stephen M. Tyszko, Richard D. Zweifel, Joseph D. Conroy, Jeremy J. Pritt, Stuart A. Ludsin. 2021. https://doi:10.1002/nafm.10647

Abstract

Management agencies commonly stock Channel Catfish Ictalurus punctatus as advanced yearlings instead of (age-0) fingerlings to help reduce potential predation mortality, despite uncertainty regarding the degree to which predation limits fingerling post-stocking survival. To better understand whether fingerling survival during the first 7 d post-stocking—when predation risk is likely greatest—could benefit from the presence of alternative prey fish, we conducted an experiment in 0.4-ha ponds (N = 18; 6 ponds/treatment) that measured fingerling (total length range = 56–186 mm) survival in ponds with predators only (adult Largemouth Bass Micropterus salmoides; 327 ± 21 mm; mean ± 1 SE), with predators and alternative prey fishes (Bluegill Lepomis macrochirus and Goldfish Carassius auratus), or with neither (i.e., control ponds). Without alternative prey, fingerling Channel Catfish survival one week (7 d) after stocking was significantly (P < 0.01) lower (89%) than in the ponds with alternative prey (98%) or in the control treatment with no predators (97%). Our experiment also indicated the potential for alternative prey to promote fingerling survival by reducing water clarity, not just by serving as a buffer from predation. Further research, however, is needed to determine the degree to which our findings apply to larger ecosystems and to learn whether stocked fingerlings survive well enough after the initial stocking period to achieve desired management goals. Even so, our results suggest that alternative prey can reduce Largemouth Bass predation mortality on fingerlings immediately after stocking, which could influence Channel Catfish stocking approaches in some managed systems.

Tracking the recruitment and evolution of snake toxins using the evolutionary context provided by the Bothrops jararaca genome

Almeida, Diego Dantas ; Viala, Vincent Louis ; Nachtigall, Pedro Gabriel ; Broe, Michael ; Gibbs, H. Lisle ; Serrano, Solange Maria de Toledo ; Moura-da-Silva, Ana Maria ; Ho, Paulo Lee ; Nishiyama-Jr, Milton Yutaka ; Junqueira-de-Azevedo, Inácio L. M. 2021. https://doi.org/10.1073/pnas.2015159118

Abstract

Venom is a key adaptive innovation in snakes, and how nonvenom genes were co-opted to become part of the toxin arsenal is a significant evolutionary question. While this process has been investigated through the phylogenetic reconstruction of toxin sequences, evidence provided by the genomic context of toxin genes remains less explored. To investigate the process of toxin recruitment, we sequenced the genome ofBothrops jararaca, a clinically relevant pitviper. In addition to producing a road map with canonical structures of genes encoding 12 toxin families, we inferred most of the ancestral genes for their loci. We found evidence that 1) snake venom metalloproteinases (SVMPs) and phospholipases A2(PLA2) have expanded in genomic proximity to their nonvenomous ancestors; 2) serine proteinases arose by co-opting a local gene that also gave rise to lizard gilatoxins and then expanded; 3) the bradykinin-potentiating peptides originated from a C-type natriuretic peptide gene backbone; and 4) VEGF-F was co-opted from a PGF-like gene and not from VEGF-A. We evaluated two scenarios for the original recruitment of nontoxin genes for snake venom: 1) in locus ancestral gene duplication and 2) in locus ancestral gene direct co-option. The first explains the origins of two important toxins (SVMP and PLA2), while the second explains the emergence of a greater number of venom components. Overall, our results support the idea of a locally assembled venom arsenal in which the most clinically relevant toxin families expanded through posterior gene duplications, regardless of whether they originated by duplication or gene co-option.

Comment on “Population genetics reveal Myotis keenii (Keen’s myotis) and Myotis evotis (long-eared myotis) to be a single species”

Ariadna E. Morales, M. Brock Fenton, Bryan C. Carstens, and Nancy B. Simmons. Can. J. Zool. 99: 415–422 (2021) dx.doi.org/10.1139/cjz-2020-0048

Abstract

Genetic exchange and hybridization appear common among the western long-eared bats from North America. Multiple sources of evidence indicate that lineages within this group are evolving independently, despite genetic exchange. However, evidence of gene flow raises questions about the species-level status of some lineages. C.L. Lausen et al. (2019. Can. J. Zool. 97(3): 267–279) proposed that Myotis evotis (H. Allen, 1864) (long-eared myotis) and Myotis keenii (Merriam, 1895) (Keen’s myotis) are one species, not two. This conclusion is based on analyses of cytochrome b and microsatellite data suggesting gene flow between these taxa. Microsatellites are not reliable markers for identifying species because homoplasy can be a major confounding factor, which appears to be true in this case. We reanalyzed the dataset of C.L. Lausen et al. (2019) and show that it is not reliable to distinguish between gene flow or homoplasy, and that these data do not support the conclusion that M. evotis and M. keenii represent a single species. Previous morphological and genomic studies indicate that these are separate species despite previous genetic exchange between them. Failing to recognize that gene flow can occur between independently evolving lineages is counterproductive for conservation because it can lead to neglect of important independent lineages, and likewise failing to use proper tools to delimit species is counterproductive to efforts to quantify biodiversity and design conservation strategies.