Phenetic and Genetic Variability of Continental and Island Populations of the Freshwater Copepod Mastigodiaptomus ha Cervantes, 2020 (Copepoda): A Case of Dispersal?

The diversity of freshwater zooplankton is still little known in Mexico, particularly in reference to insular zooplankton communities. Diaptomid copepods (Crustacea: Copepoda: Calanoida) are a widespread group worldwide, and Mexico harbours high diaptomid diversity. Based on a recent sampling of freshwater zooplankton on a Caribbean Island of Mexico, we present the first record of a diaptomid copepod from an island freshwater ecosystem. It shows the well-known tendency of Neotropical diaptomids to have restricted distributional patterns and high levels of endemism. The species recorded, Mastigodiaptomus ha (Cervantes-Martínez, 2020) appears to have a restricted distribution in the Yucatan Peninsula (YP), and the island as well. In order to explore potential differences between the island and continental populations of this species, its phenetic and genetic diversity was analysed by performing morphological comparisons and also by exploring differences of the habitat conditions and genetic sequences (CO1 gene). Our analysis revealed a low (average = 0.33%) genetic divergence between both populations; likewise, both the morphology and habitat conditions closely resemble each other in these two populations. The low genetic divergence between the continental and island populations of M. ha suggests an early common origin of the species in the geological history of the YP.

Multi-scale and multi-system perspectives of zooplankton structure and function in Canadian freshwaters

This review provides a Canadian perspective on freshwater zooplankton diversity and ecology across scales and systems. It aims at describing how zooplankton is a source of biodiversity in forms and functions, a key component of plankton food web, a model for ecological theories and a sentinel for monitoring lake ecological integrity and function facing environmental changes and anthropogenic stressors. These objectives are addressed across a continuum of spatial scales and ecosystem types. Zooplankton communities demonstrated a wide range of responses to anthropogenic disturbances across scales and systems due to interactions with watershed biogeochemistry and climate. This review supports the Multiple Forces hypothesis where forcing by abiotic factors have a primordial role at global scale over Canadian ecoregions, and at regional scale in the Boreal ecozones. In contrast, forcing by biotic factors is more influential at local scale, in resort and urban regions. Future research challenge will be to combine all new concepts and approaches in a holistic perspective to examine the response of freshwater zooplankton to multiple environmental changes and anthropogenic stressors.

Breaking Free from Thermodynamic Constraints: Thermal Acclimation and Metabolic Compensation in a freshwater zooplankton species

Ectothermic organisms’ respiration rates are affected by environmental temperatures, and sustainable metabolism at high temperatures sometimes limits heat tolerance. Organisms are hypothesized to exhibit acclimatory metabolic compensation effects, decelerating their metabolic processes below Arrhenius expectations based on temperature alone. We tested the hypothesis that either heritable or plastic heat tolerance differences can be explained by metabolic compensation in the eurythermal freshwater zooplankton crustacean Daphnia magna. We measured respiration rates in a ramp-up experiment over a range of assay temperatures (5 °C - 37 °C) in 8 genotypes of Daphnia representing a range of previously reported acute heat tolerances and, in a narrower range of temperatures (10 °C - 35 °C), in Daphnia with different acclimation history (either 10°C or 25°C). We discovered no difference in temperature-specific respiration rates between heat tolerant and heat-sensitive genotypes. In contrast, we observed acclimation-specific compensatory differences in respiration rates at both extremes of the temperature range studied. Notably, there was a deceleration of oxygen consumption at higher temperature in the 25°C-acclimated Daphnia relative to their 10°C-acclimated counterparts, observed in active animals, a pattern corroborated by similar changes in filtering rate and, partly, by changes in mitochondrial membrane potential. A recovery experiment indicated that the reduction of respiration was not caused by irreversible damage during exposure to a sublethal temperature. Response time necessary to acquire the respiratory adjustment to high temperature was lower than to low temperature, indicating that metabolic compensation at the lower temperatures require slower, possibly structural changes.