Effects of daily thermal fluctuations on the Atlantic silverside, a fish with temperature-dependent sex determination.

Temperature-dependent sex determination (TSD) occurs when the temperature during development affects gonad determination. Historically, most work on TSD in fishes was conducted under constant temperatures, yet daily fluctuating temperatures can significantly alter fish physiology and life history. Thus, we subjected the Atlantic silverside, Menidia menidia (a TSD species), to 28, 28 ± 2 and 28 ± 4°C (a high, masculinizing temperature) and quantified sex ratios and length. We found that the percentage of females increased by 60%-70% when the fish were exposed to daily fluctuating temperatures (from 10% to 16% and 17% under fluctuations).

Natural variation on whole-plant form in the wild is influenced by multivariate soil nutrient characteristics: natural selection acts on root traits.

PREMISE: In the complex soil nutrient environments of wild populations of annual plants, in general, low nutrient availability restricts growth and alters root-shoot relationships. However, our knowledge of natural selection on roots in field settings is limited. We sought to determine whether selection acts directly on root traits and to identify which components of the soil environment were potential agents of selection. METHODS: We studied wild native populations of Arabidopsis thaliana across 4 years, measuring aboveground and belowground traits and analyzing soil nutrients. Using multivariate methods, we examined patterns of natural selection and identified soil attributes that contributed to whole-plant form. In a common garden experiment at two field sites with contrasting soil texture, we examined patterns of selection on root and shoot traits. RESULTS: In wild populations, we uncovered selection for above- and belowground size and architectural traits. We detected variation through time and identified soil components that influenced fruit production. In the garden experiment, we detected a distinct positive selection for total root length at the site with greater water-holding capacity and negative selection for measures of root architecture at the field site with reduced nutrient availability and water holding capacity. CONCLUSIONS: Patterns of natural selection on belowground traits varied through time, across field sites and experimental gardens. Simultaneous investigations of above- and belowground traits reveal trait functional relationships on which natural selection can act, highlighting the influence of edaphic features on evolutionary processes in wild annual plant populations.

Microplastic and tire wear particle occurrence in fishes from an urban estuary: Influence of feeding characteristics on exposure risk.

The influence of feeding behavior and feeding ecology on microplastic occurrence in fishes in an urbanized estuary was studied by surveying microplastics in the digestive tracts (gut) of five fish species: the planktivorous Bay Anchovy and Atlantic Menhaden, the piscivore Spotted Seatrout, the benthivore Spot and the detritivore/benthivore Striped Mullet. Microplastics were found in 99% of fishes collected with an average of 27 microplastics per individual fish, 6 microplastics per gram of fish, and 21 microplastics per gram of gut, although exposure varied among species. Atlantic Menhaden possessed significantly more microplastic per fish weight than other species, which may be attributed to their regular ingestion of marine snow aggregates. Fibers were the most common type of microplastic in all fishes, and suspected tire wear particles were found in 14% of individuals across all five species, constituting the first evidence of tire wear particle consumption in field-collected organisms.