Sex‐specific life history responses to nymphal diet quality and immune status in a field cricket

Individual fitness is expected to benefit from earlier maturation at a larger body size and higher body condition. However, poor nutritional quality or high prevalence of disease make this difficult because individuals either cannot acquire sufficient resources or must divert resources to other fitness‐related traits such as immunity. Under such conditions, individuals are expected to mature later at a smaller body size and in poorer body condition. Moreover, the juvenile environment can also produce longer‐term effects on adult fitness by causing shifts in resource allocation strategies that could alter investment in immune function and affect adult lifespan. We manipulated diet quality and immune status of juvenile Texas field crickets, Gryllus texensis, to investigate how poor developmental conditions affect sex‐specific investment in fitness‐related traits. As predicted, a poor juvenile diet was related to smaller mass and body size at eclosion in both sexes. However, our results also reveal sexually dimorphic responses to different facets of the rearing environment: female life history decisions are affected more by diet quality, whereas males are affected more by immune status. We suggest that females respond to decreased nutritional income because this threatens their ability to achieve a large adult body size, whereas male fitness is more dependent on reaching adulthood and so they invest in immunity and survival to eclosion.     

Responses of rhizome length and ramet production to resource availability in the clonal sedge <Emphasis Type="Italic">Scirpus olneyi</Emphasis> A. Gray

The clonal plant Scirpus olneyi has two types of ramets within one clone; a ramet with a very long rhizome (LRR) and a ramet with a very short rhizome (SRR). Based on foraging theory of clonal plants, we hypothesised that these two types of ramets were functionally specialised to different tasks: the task of LRRs is for exploring while SRRs is for consolidating the patches. We also hypothesised that LRRs tended to produce LRRs continuously during a growing season to reach further patches while SRRs tended to produce SRRs fewer times to stay in the same patches. To evaluate these hypotheses, we analysed the sequence of two ramets of plants growing in four communities in the field and five treatments in garden experiments. In the garden experiments, plants in high quality treatments (e.g. low salinity, full sun, and sufficient nutrient) produced proportionally more SRRs and branched more frequently than plants in low quality treatments (e.g. strong salinity or less light or less nutrient). LRRs kept producing LRRs in every treatment, but LRRs in low quality treatments produced less SRRs than LRRs in high quality treatments did. The field observations showed LRRs kept producing LRRs in every community in the same growing season, but SRRs production varied among communities. In the communities with larger biomass and high SRR ratio, LRRs produced more SRRs and those SRRs produced proportionally more SRRs. On the other hand, in the communities with smaller biomass and low SRR ratio, LRRs produced less SRRs and those SRRs produced proportionally less SRRs. The results of garden experiments and field observations support our hypotheses. Two ramets are functionally specialised to perform different tasks. And their production patterns are suitable to perform their tasks. And their production patterns are suitable to perform their tasks: the sequential production of LRRs allows plants to have higher chance to reach new locations, and the limited but sequential production of SRRs allows plants to consolidate the patches. The observed production patterns of two ramets are associated with phalanx and guerrilla strategies by Lovett Doust, and S. olneyi shows both strategies within relatively small scale environments.     

Increased activity and growth rate in the non‐dispersive aquatic larval stage of a damselfly at an expanding range edge

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