Abstract
Desiccation is a particular risk for small animals in arid environments. In response, many organisms “construct niches,” favorable microenvironments where they spend part or all of their life cycle. Some maintain such environments for their offspring via parental care. Insect eggs are often protected from desiccation by parentally derived gels, casings, or cocoons, but active parental protection of offspring from desiccation has never been demonstrated. Most free-living thrips (Thysanoptera) alleviate water loss via thigmotaxis (crevice seeking). In arid Australia, Acacia thrips (Phlaeothripidae) construct many kinds of niche. Some thrips induce galls; others, like Dunatothrips aneurae, live and breed within “domiciles” made from loosely glued phyllodes. The function of domiciles is unknown; like other constructed niches, they may 1) create favorable microenvironments, 2) facilitate feeding, 3) protect from enemies, or a combination. To test the first 2 alternatives experimentally, field-collected domiciles were destroyed or left intact. Seven-day survival of feeding and nonfeeding larval stages was monitored at high (70–80%) or low (8–10%, approximately ambient) humidity. Regardless of humidity, most individuals survived in intact domiciles, whereas for destroyed domiciles, survival depended on humidity, suggesting parents construct and maintain domiciles to prevent offspring desiccating. Feeding and nonfeeding larvae had similar survival patterns, suggesting the domicile’s role is not nutritional. Outside domiciles, survival at “high” humidity was intermediate, suggesting very high humidity requirements, or energetic costs of wandering outside domiciles. D. aneurae commonly cofound domiciles; cofoundresses may benefit both from shared nestbuilding costs, and from “deferred byproduct mutualism,” that is, backup parental care in case of mortality.
Highlights
Desiccation is a common environmental hazard in terrestrial habitats (e.g., Schmidt-Nielsen 1997), most especially in arid zones (Whitford 2002)
Almost all individuals remaining inside intact domiciles (IH1 and IL1) survived until experiment 1 was terminated at 182 h, regardless of humidity (Figure 2a)
As expected from the findings presented above, larvae died more quickly after exiting domiciles in the low humidity treatment than in the high humidity treatment in both experiments
Summary
Desiccation is a common environmental hazard in terrestrial habitats (e.g., Schmidt-Nielsen 1997), most especially in arid zones (Whitford 2002). For insects and other small-bodied animals, with large surface area:volume ratios, desiccation risk in arid environments is acute (Schmidt-Nielsen 1984; Chown et al 1995; Le Lagadec et al 1998). While most insects abandon offspring, many construct nests or otherwise actively modify the environment to help offspring develop (reviewed in Costa 2006). Parental arthropods sometimes produce or construct niches to reduce desiccation via, for example, cocoons in spiders (Hieber 1992 and references therein), the bags of bagworms (Rivers et al 2002), oothecae in mantises (Birchard 1991), and a gelatinous matrix in Limnephilid caddisflies inhabiting vernal pools (Wiggins 1973). Though, there has to my knowledge been no demonstration of active parental behavior
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