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

Abstract

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.

Aberrant clones: Birth order generates life history diversity in Greater Duckweed, Spirodela polyrhiza

“…exhibit diminishing fitness with birth order; if this holds for S. polyrhiza , the switch to turion production in late birth‐order fronds with decreasing residual reproductive value may be a low‐cost solution for variance generation. Interest in the adaptive significance of the expression of individual phenotypic variance (Bull, ; Simons & Johnston, ) has recently intensified (Abley et al., ; New et al., ; Rossi, Gandolfi, & Menozzi, ; Stelkens, Miller, & Greig, ; Xue & Leibler, ), and has become topical in fields such as medicine ( e.g., Rovira‐Graells et al., ) and human psychology (Hertler, ). The effects of birth order on life history phenology observed in the present study provide an additional source of individual, or within‐genotype variance expression; however, inferences about the adaptive significance of this phenological variation in the field will require further study.…”

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

“…This model assumed that the eggs did not die until they reached the maximum age (E 54 ) but that all remaining eggs died after the maximum age. These assumptions did not reflect the real situation, in which some of the deposited eggs became discolored and unviable before hatching . Nevertheless, because there were no available data on age‐specific egg survival rates, these conservative assumptions were used.…”

“…The hatching rate h i at egg stage i was obtained from all available data in 4 studies where no ostracods were exposed to toxic chemicals [12,13,15,17]. Table 1 shows the summary of 5 hatching scenarios (A-E).…”

“…Heterocypris incongruens produces some long‐dormant (diapausing) eggs (> 150 d for hatching) as well as early eggs that hatch within 30 d after laying . Egg development time is influenced by factors such as photoperiod, temperature, genotype differences, and maternal effects and thus cannot be well predicted by the egg size . The net reproductive rate ( R 0 ; number of hatchlings per female) is a frequently used endpoint in life‐cycle tests; nevertheless, the long monitoring of egg development over 150 d is not practical for a routine toxicity assessment.…”

Birth order as a source of diversification in spring phenology and its potential effects on performance in greater duckweed, Spirodela polyrhiza

“…While seasonal change is generally deterministic, interannual variation in the timing and mangitude of environmental change can be highly stochastic (Proulx and Day 2002;Wang and Dillon 2014;Botero et al 2015;Noh et al 2017); for example, the timing of first snow melt in higher latitudes can vary greatly from year to year (Van Vuren and Armitage 1991;Stinson 2004). This is the unpredictable component of environmental variation and it presents a challenge for organismal survival (Simons 2014;Furness et al 2015;Rossi et al 2017;Tarazona et al 2017).…”