Temporal environmental change, clonal physiology and the genetic structure of aDaphniaassemblage (D. galeata–hyalinahybrid species complex)

Abstract

1. In a combined field and laboratory study, seasonal relationships between water temperature and oxygen content, genetic structure (composition of MultiLocus Genotypes, MLGs) of a Daphnia assemblage (D. galeata-hyalina hybrid species complex), and the physiological properties of clones of frequent MLGs were studied. In accordance with the oxygen-limited thermal tolerance hypothesis, essential physiological variables of oxygen transport and supply were measured within the tolerable temperature range. 2. A few MLGs (types T1-T4) were frequent during early spring and late autumn at surface temperatures below 10°C. Clones of T1-T4 showed a low tolerance towards higher temperatures (above 20°C) and a high phenotypic plasticity under thermal acclimation in comparison to clones derived from frequent MLGs from later seasons, and stored highmedium quantities of carbohydrates at 12 and 18°C. 3. Another MLG (T6) succeeded the MLGs T1-T4. T6 was frequent over most of the year at temperatures above 10°C and below 20°C. A clone derived from T6 exhibited a high tolerance towards warm temperatures and a more restricted phenotypic plasticity. It stored high-medium quantities of carbohydrates at 12, 18 and 24°C and showed a high capacity for acclimatory adjustments based on haemoglobin expression. 4. During the summer period at temperatures ‡20°C, the MLG T6 was found mainly near to the thermocline, where temperature and oxygen content were distinctly lower, and to a lesser extent in surface water. At the surface, another MLG (T19) was predominant during this period. A clone of this MLG showed a very high tolerance towards warm temperatures, minimal phenotypic plasticity, low carbohydrate stores and a high capacity for circulatory adjustments to improve oxygen transport at higher temperatures. 5. This study provides evidence for connections between the spatio-temporal genetic heterogeneity of a Daphnia assemblage and the seasonal changes of water temperature and oxygen content. The data also suggest that not only the actual temperature but also the dynamics of temperature change may influence the genetic structure of Daphnia populations and assemblages.

The response of temperate aquatic ecosystems to global warming: novel insights from a multidisciplinary project

“…In addition, the genetic composition of the population differed substantially between cold-and warm winter years (Zeis et al 2010). This will affect physiological capabilities of the spring population to cope with high temperature and/or low oxygen (Pinkhaus et al 2007;Paul et al 2012), life history strategies, and potentially also the inducibility of defense strategies against predators (Hülsmann and Wagner 2007).…”

Seasonal and interannual changes in water temperature affect the genetic structure of a Daphnia assemblage (D. longispina complex) through genotype‐specific thermal tolerances

“…These variables included (1) ventilation rate, i.e., the movement frequency of the thoracic limbs, which serve for filter feeding as well as ventilatory oxygen transport (Pirow et al 1999;Pirow and Buchen 2004); (2) heart rate, which is related to the circulatory oxygen transport rate (Bä umer et al 2002;Seidl et al 2005a,b); and (3) nicotinamide adenine dinucleotide (NADH) fluorescence intensity from leg muscles, which is indicative of the mitochondrial reduction-oxidation state and oxygen supply of these tissues (Pirow et al 2001).…”

“…The optophysiological setup was described by Pirow et al (2001) and Pinkhaus et al (2007). For the different CLs and acclimation temperatures, replicated experiments were carried out (at least three different individuals) on single females with carapace lengths (Seidl et al 2005b) of 1.25-1.32 mm and carrying 3-5 parthenogenetic embryos of developmental stages 1-2 (Green 1956).…”

“…For the different CLs and acclimation temperatures, replicated experiments were carried out (at least three different individuals) on single females with carapace lengths (Seidl et al 2005b) of 1.25-1.32 mm and carrying 3-5 parthenogenetic embryos of developmental stages 1-2 (Green 1956). Handling of the tested individuals and the experimental protocol follow Pinkhaus et al (2007). Briefly, animals were incubated for 30 min in M4 medium before experimentation and then immobilized by gluing their dorsal carapace with adhesive to a thin insect needle attached to a small polyvinyl chloride cube.…”

“…A 1-yr study on the D. longispina complex from Saidenbach Reservoir (Pinkhaus et al 2007) provided evidence for connections between the genetic spatiotemporal heterogeneity of the Daphnia assemblage and seasonal changes in water temperature. A 2-yr study on the same species complex (Schwerin et al 2010) focused on hemoglobin function in Daphnia from the field.…”