Thematic session.
Lead Organizer: Nandini Sarma, FES Iztacala, UNAM (nandini@unam.mx)
Co-organizers:
S. S. S. Sarma, FES Iztacala, UNAM (sarma@unam.mx)
Presentations
04:30 PM
FORMATION OF POPULATION GENETIC STRUCTURE AND MAINTENANCE OF HAPLOTYPE COEXISTENCE IN OBLIGATE PARTHENOGENETIC DAPHNIA CF. PULEX IN A SMALL POND (10631)
Primary Presenter: Yurie Otake, Kyoto University (otake.y02@gmail.com)
How the population genetic structure changes during colonization in a novel habitat has been a main topic in ecology. Lakes, as semi-closed systems, have been effective model environments for studying it. However, genetic changes during early colonization remain poorly understood because early-stage populations are rarely observed. Using a paleolimnological approach with diapausing eggs, we revealed the long-term dynamics of an obligate parthenogenetic Daphnia cf. pulex population in Lake Fukami-ike, Japan. Furthermore, we examined the mechanisms underlying haplotype coexistence. Paleolimnological analyses revealed that the D. cf. pulex population established and persisted with one predominant haplotype and limited genetic diversity. In recent years, genetically distant haplotypes from a predominant one appeared but did not replace the predominant one. We tried to understand how these lineages coexist, focusing on the Storage effect. Laboratory experiments showed the recently appeared haplotype tended to produce diapausing eggs in broader environmental conditions than the predominant one. Empirically parameterized theoretical analyses suggested that different photoperiodic responses can promote coexistence via the storage effect when the growing season length fluctuates. Overall, our study suggests that an obligate parthenogenetic population can establish and persist even with limited genetic diversity, a condition generally considered to constrain adaptation in novel habitats. We also suggest that variation in diapause-induction timing may facilitate coexistence between genetically distant haplotypes.
04:45 PM
EFFECTS OF NUTRIENT LIMITATION ON MICROALGAL COMPOSITION AND NUTRITIONAL QUALITY TO A COPEPOD CONSUMER (10666)
Primary Presenter: Ann Tarrant, Woods Hole Oceanographic Institution (atarrant@whoi.edu)
Nutrient limitation structures the taxonomic composition, abundance, and physiology of producers, and consequently the prey abundance and quality available to consumers. While some types of marine microalgae are strictly autotrophic, others are able to ingest particles in a form of mixotrophy. It has been proposed that mixotrophs have more stable nutrient stoichiometry under variable/limiting nutrient conditions, which could make them a particularly valuable nutritional resource. We reared microalgal taxa under nutrient replete and nutrient limiting conditions and measured particle ingestion and biochemical composition. The chlorophyte Dunaliella sp. unexpectedly exhibited mixotrophy and maintained stable stoichiometry under low-nutrient conditions. Pyramimonas parkeae, Heterocapsa triquetra, Rhodomonas salina and Thalassiosira weissflogii exhibited more variable nutrient stoichiometry. These algal strains were tested as prey for the copepod Centropages typicus through multi-day feeding experiments with adult females. At high food levels (>400 ugC/L), most prey reared under nutrient-limited and -replete conditions supported similar levels of egg production by C. typicus. However, egg production decreased in copepods fed nutrient-limited diatoms (T. weissflogii) and increased in those fed nutrient-limited R. salina. Overall, our results show that even with high levels of food, C. typicus reproduction is sensitive to nutrient limitation of strictly autotrophic prey, but robust to moderate stoichiometric changes in potentially mixotrophic prey.
05:00 PM
COMPARING TWO METRICS OF THERMAL TOLERANCE TO QUANTIFY THE EFFECTS OF STARVATION ON THERMAL LIMITS IN A COMMON COPEPOD (10771)
Primary Presenter: Rowan Batts, University of Connecticut (rowan.batts@uconn.edu)
Several techniques are used to quantify thermal limits in aquatic species. The Critical Thermal maximum (CTmax) is a common technique that uses a loss of response to stimulus as an endpoint under rapid, acute temperature ramping. In contrast, other studies use mortality under exposure to a constant temperature to quantify the thermal limit. Due to the shorter duration of thermal stress, CTmax gives a higher thermal limit than most mortality-based metrics. Thermal limits are often reported using only a single method per study; therefore, a more robust understanding of the relationship between thermal tolerance techniques is needed. We measure the thermal tolerance of a common coastal copepod, Acartia tonsa, using CTmax and Lethal Temperature 50 (LT50, the temperature at which mortality is 50% after 24 hours of exposure) under food replete and starvation conditions. We found that CTmax was ~ 35.5°C for both treatments and unaffected by starvation. LT50, however, was significantly affected by starvation with starved individuals seeing an LT50 of 25.8°C compared to 30.5°C for the food replete treatment. Temperatures at our collection site can exceed 26°C, meaning that short term food limitation can cause mass mortality at ecologically relevant temperatures, a finding that is not illustrated in CTmax measurements alone.
05:15 PM
DRIVERS OF ZOOPLANKTON BODY SIZE IN PONDS ACROSS BROAD SPATIAL SCALES (11018)
Primary Presenter: Sandra Brucet, University of Vic & ICREA (sandra.brucet@uvic.cat)
Body size is a fundamental trait influencing ecological functions, trophic dynamics and organismal fitness across ecosystems. However, the environmental drivers shaping body size patterns in pond ecosystems across broad spatial scales remain poorly defined. We assessed how latitude, food availability and predation influence individual body size in cladocerans and copepods, as well as the size structure of the entire zooplankton community. Zooplankton was sampled using standardized protocols in 141 ponds across four European countries and Uruguay. Our findings indicate that latitude and predation are major selective forces shaping crustacean individual body size in ponds. Individual mean body size increased with latitude for both taxa, supporting the temperature-size rule, while fish presence was associated with smaller body sizes. In contrast, the entire zooplankton community size structure was mainly shaped by local factors and did not significantly differ along the climatic gradient. Steeper size spectra with increasing chlorophyll‑a concentrations reflected dominance of small-sized zooplankton. This suggests reduced energy transfer efficiency to higher trophic levels and weaker top-down control on phytoplankton in more eutrophic conditions. Conversely, flatter slopes at lower chlorophyll-a concentrations suggest a greater contribution of larger zooplankton and stronger top-down control. The overall intercept of size spectra was higher in deeper, vegetated ponds, indicating higher total zooplankton abundance. These results highlight the value of size-based approaches for understanding pond food-web functioning and their responses to environmental stressors.
05:30 PM
BIODIVERSITY OF CRUSTACEAN ZOOPLANKTON IN THE ST. LOUIS RIVER ESTUARY OF WESTERN LAKE SUPERIOR (11046)
Primary Presenter: Michael Nagel, University of Minnesota Duluth (nage0138@d.umn.edu)
Zooplankton communities are indicators of environmental stressors such as climate, invasive species introduction, and other anthropogenic influences on water quality. The St. Louis River estuary on the Western tip of Lake Superior is important ecologically as the largest US tributary into Lake Superior. Industrially, it is also the location of the most active Great Lakes cargo shipping port and is the largest receiver of inter-lake ballast water, the vector by which numerous aquatic invasive species (AIS) have become established in the region. In 2008, ballast water exchange was fully implemented for vessels travelling internationally into the Great Lakes as a means of reducing movement of AIS from other locations. We sampled in 2007/2008 to establish a baseline of zooplankton biodiversity in the estuary and resampled the same locations in 2024/2025 to assess differences before and after ballast water policy changes. In both pairs of years, we conducted semi-weekly sampling comprising vertical zooplankton net tows (100-µm mesh) and a suite of water quality parameters from roughly April to September. We visited nine locations through varying habitats and levels of industrialization and shipping activity. Spatial and temporal variability in zooplankton communities will be assessed as a function of habitat development with a focus on biodiversity and abundance.
05:45 PM
SEASONAL POPULATION DYNAMICS OF ZOOPLANKTON AND THEIR PARASITE COMMUNITIES IN LAKES OF SOUTHERN ALBERTA (11136)
Primary Presenter: Molly Tilley, University of Lethbridge (m.tilley@uleth.ca)
Parasite epidemics within zooplankton hosts can shape aquatic food web structure and functioning, potentially affecting higher trophic levels. Identifying the controls and consequences of epidemics can thus enhance our understanding of the ecology of aquatic systems. The parasite populations and communities in zooplankton are thought to be shaped by complex controls related to seasonal changes in the biotic and abiotic environment, including nutrient availability, mixing and resuspension of parasite infective stages, temperature-dependent release and viability of free-living parasite stages, and host population dynamics. These controls not only affect the parasites themselves, but also how they are transmitted from host to host. Yet, despite the potential limnological importance of parasites, our understanding of zooplankton-parasite interactions is limited. Past research has typically focused on select microparasite taxa and a limited set of environmental factors, making it difficult to draw conclusions about community-level interactions and their controls. Here, we explored the seasonal patterns of zooplankton-parasite community dynamics in four eutrophic lentic ecosystems (lake, reservoir and open water wetland ecosystems) in a heavily agriculturalized and effluent-impacted aquatic network in southern Alberta, Canada. We sampled the meso-zooplankton communities seasonally in each ecosystem, for enumeration and identification of zooplanktonic hosts and their parasites. Water quality conditions, including vertical profiles of limnological conditions (i.e., temperature, dissolved oxygen) were also measured. Our presentation will summarize our results and provide new insights into seasonality of both micro- and macroparasites associated with zooplankton, and how these associations vary across distinct ecosystems.
CS007B Zooplankton Ecology and Physiology
Description
Time: 4:30 PM
Date: 14/5/2026
Room: 520E