Early and late maternal effects on hatching phenology of Heterocypris incongruens (Crustacea: Ostracoda)

To sleep or not to sleep: Dormancy and life history traits in Eucypris virens (Crustacea, Ostracoda)

Dormancy represents an investment with its own costs and benefit. Besides the advantage obtained from the avoidance of harsh environments and from the synchronization of life cycles with seasonal changes, an organism could benefit from a temporary stop in growth and reproduction. To test this hypothesis a transgenerational experiment was carried out comparing the life history traits of clonal females of Eucypris virens from resting and non-resting eggs at two different photoperiods: short day length (6:18 L:D), proxy of favorable but unpredictable late winter-spring hydroperiod, and long day length (16:8 L:D) proxy of dry predictable unfavorable season, inducing resting egg production and within-generation plasticity (WGP). Clonal females that were dormancy deprived showed the highest age at first deposition and the lowest fecundity. Dormancy seems to work as a resetting mechanism of reproduction. Transgenerational plasticity (TGP) had a bounce back pattern: the phenotype of F1 generation was influenced by cues experienced in the F0 generation but the effects of F0 exposure were not evident in the F2. TGP might be adaptive when a mother experiences some kind of seasonality or stochasticity producing both resting and nonresting eggs. A positive relationship between the number of resting eggs and the total number of eggs per females suggested the absence of trade-off between dormancy and reproduction. Both WGP and TGP increase the mother long term fitness with important consequences on population dynamics, on the way a species spread throughout space and time and might respond to climate change.

Duration of life-cycle toxicity tests with the ostracod Heterocypris incongruens

An acute sediment toxicity test using the ostracod Heterocypris incongruens is user friendly and has high sensitivity; however, a life-cycle test using this species has not been developed. The most challenging problem when developing a life-cycle test is that the egg development time varies greatly and is sometimes too long (> 150 d) to monitor. It is desirable to shorten the duration of life-cycle toxicity tests including the observation period of egg development while preserving the ecological relevance of the net reproductive rate (R₀ ), an endpoint in the life-cycle test. Therefore, in the present study, we suggest a practical test duration for R₀ using population growth rate (λ) as a measure of ecological relevance. We collected a range of life history characteristics of the ostracod by combining data from the literature and experimental results, constructed population matrix models, and calculated λ for 20 life history patterns. The results showed that a longer test period (> 150 d) did not increase the correlation coefficients between R₀ and λ. Rather, a shorter test duration resulted in R₀ being highly correlated with λ. Our results suggest that a life-cycle toxicity test using the ostracod can provide an ecologically relevant toxicity endpoint, even if the test is abandoned after approximately 50 d and unhatched eggs remain. Environ Toxicol Chem 2017;36:3443-3449. © 2017 SETAC.

Development of a chronic sediment toxicity test using the benthic ostracod Heterocypris incongruens and their application to toxicity assessments of urban road dust

This study reports on the development and application of a chronic sediment toxicity test using the benthic ostracod Heterocypris incongruens. H. incongruens reproduction parameters such as egg production, first day of brooding, egg-laying ratio, and hatching ratio were examined in this study. The test was first validated by determining the repeatability of the test method under seven control performances. The results showed good test repeatability of most endpoints, with coefficient of variation (CV) results below 15%. However, lifetime egg production, hatching ratio, and the reproductive rate were highly variable, with CVs ranging from 29.5% to 51.9%. Next, an application example of the proposed chronic method was performed using a series of urban road dust (URD) samples diluted with a reference sediment and compared to a 6 d H. incongruens toxicity test. The results of the proposed chronic test showed a statistically significant difference in the first day of brooding at 6.25% URD which did not exhibit significant mortality and growth inhibition in 6 d toxicity test.

Mother's Age and Hatching Phenology Strategy of Heterocypris incongruens (Crustacea: Ostracoda) in Unpredictable Environment

We report experimental evidence of egg polyphenism in clonal lineages of Heterocypris incongruens from an ephemeral pond on a Mediterranean Island (Lampedusa, Italy). In controlled laboratory conditions, clonal females produced three different kinds of eggs: (i) resting and desiccation-resistant eggs, (ii) nonresting eggs that hatched gradually within 2 month hydroperiod, and (iii) nonresting delayed development eggs that hatched synchronously. Clonal females showed a diversified bet-hedging strategy to spread risk of reproduction in ponds with unpredictable hydroperiod. They adjusted proportion of different egg phenotypes in response to experimental temperature and photoperiod that are proxies for different hydroperiod unpredictability. The proportion of resting eggs is not affected by maternal age at deposition, but mother's age has a key role in defining the development time and the hatching phenology of nonresting eggs. Genetically identical eggs kept at the same controlled laboratory conditions showed a U-shaped distribution of development time. Development time variance decreased with mother's age at deposition. The resulting wedge-shaped relationship between development time and mother's age at deposition may be interpreted by considering mother's age as a proxy for the probability of drought onset. The older the mother, the shorter the latency to drought and the shorter is the time for nonresting eggs to hatch. Considering only the delayed development of eggs that hatch synchronously, development time is inversely related to the mother's age at deposition: this relationship generates the observed hatching peak.

Seasonal niche partitioning and coexistence of amphimictic and parthenogenetic lineages of Heterocypris barbara (Crustacea: Ostracoda)

Sympatry of amphimictic and parthenogenetic lineages in species with mixed reproductive systems is rarely observed in nature. On Lampedusa Island (Pelagie Islands, Italy), amphimictic and parthenogenetic lineages of Heterocypris barbara (Gauthier and Brehm, 1928) co-occur in a temporary pond. Their sympatric persistence calls for an ecological differentiation. We investigated the role of seasonal variation of temperature and photoperiod conditions by two different approaches: microcosms set up by inundation of dry sediments from the temporary pond and life-table experiments. Microcosms recreate conditions similar to the field and in their sediments random samples of resting eggs of both amphimictic and parthenogenetic females are stored. Life-table experiments supplied individual-based estimates of survivorship, adult life span, fecundity, and sex ratio in the progeny. We carried out the experiments at 24 °C and a photoperiod of 12 h light (L) : 12 h dark (D) (simulating fall conditions) and at 16 °C and a photoperiod of 10 h L : 14 h D (simulating winter conditions). Males and amphimictic females were the most numerous forms at 24 °C and 12 h L : 12 h D; parthenogenetic females were dominant at 16 °C and 10 h L : 14 h D. Life-table experiments showed that amphimictic forms do not complete development at 16 °C and 10 h L : 14 h D. Our results suggest that sympatry of amphimictic and parthenogenetic females in the field depends on seasonal niche partitioning and the storage effect of resting eggs that allows survival through adverse-season conditions.