Different Pathways in Arthropod Postembryonic Development

Abstract

Abstract.-To investigate the consequences of canalization and plasticity in arthropod developmental pathways, we developed a model that predicts eight possible combinations among three larval developmental parameters. From the descriptions of insect and spider postembryonic development, it is apparent that not all aspects of juvenile development are plastic and that species differ in which traits are plastic. Most strikingly, only four of the possible eight combinations of canalized and plastic parameters have been found in nature. Using this model, we show that the identity of the canalized developmental parameters and the degree of genetic variation in the value at which a given parameter is fixed have important implications for the ecology and evolution of complex life cycles.Key words.-Arthropods, canalization, constraint, growth, plasticity, postembryonic development.Received December I, 1994.The age and size at which an individual becomes mature are very important determinants of its fitness, and the ultimate, evolutionary causes of variation in both have long attracted attention (e.g., Stearns 1992 and references therein). Both genetic variation and environmentally induced variation (plasticity) can significantly alter the age and size at which an individual matures, but the ecological and evolutionary consequences of genetic versus plastic causes of variation are very different (Caswell 1983;Via and Lande 1985;Gomulkiewicz and Kirkpatrick 1992). Environmentally induced differences among adults are important measures of plasticity (e.g., Stearns and Koella 1986;Solbreck et al. 1989;Hillesheim and Stearns 1991), but these are emergent properties of the juvenile developmental parameters. The relative importance of genetic variation and plasticity in determining age and size at maturity 'can be better understood by investigation of juvenile development (Schmalhausen 1949;Reznick 1990;Gomulkiewicz and Kirkpatrick 1992;Bernardo 1993). In complex life cycles, juvenile developmental plasticity may playa vital role in the interaction of the life cycle with temporal and spatial variation in habitat quality. However, not all aspects of development are plastic; some are canalized. Species and populations differ in which traits are plastic, and such differences can significantly affect the ability of the organism to compensate for poor growing conditions. In the model of juvenile development presented herein, we describe different combinations of canalized and plastic developmental parameters found in arthropods, and we discuss the ecological and evolutionary consequences of various patterns of plasticity.Arthropods are ideal for life-history studies because growth and developmental stage are easily quantified. The juvenile period is broken into discrete stages (instars). In most insects and spiders, growth is determinate, and the molt into the adult stage is the final molt, after which the sclerotized body parts grow no further. Thus, size at maturity is determined by the number of stages and growth in each molt. Li...

Nutrients intake determines the post-maturity molting in the golden orb-web spider Nephila pilipes (Araneae: Nephilidae)

“…Studies on Nephila clavipes showed that the number of molts and inter-molt duration were plastic as a result of variation in food resources (Higgins and Rankin, 1996). The results of our study showed that adult female N. pilipes also adjust molting to variations in foraging success, possibly maximizing their reproductive potential.…”

Sexual cannibalism in Nephila plumipes as a consequence of female life history strategies

“…This result may be because of the constraints of moulting. Females in good condition may not be able to convert all of their resources into growth of the sclerotized body parts because expansion of these structures is limited (Higgins & Rankin, 1996; Hutchinson et al ., 1997 and references therein). As a consequence, females with a rich feeding history may carry accumulated resources into the following instar, thereby allowing them to moult again sooner.…”

Large size as an antipredator defense in an insect

“…The present study raises the question of why variation in instar number exists in this species. Proximate explanations of this variation point to various environmental and genetic influences (Higgins & rankin 1996;esperk et al 2007;González-Suárez et al 2011;Chown & Gaston 2010). One such environmental influence is food availability during development (esperk et al 2007).…”

“…In nature, therefore, the consistent negative relationship between adult female pronotum length and adult emergence date in S. limbata might be a reflection of the following factors: a narrow window for hatching and, for a given developmental pattern, slowly-growing individuals emerging as adults later and smaller. a critical time in the season, by which immatures must mature in order to reproduce, might compel slow-growers to emerge at particularly small sizes, thereby generating a even stronger negative relationship between adult length and emergence date (Higgins & rankin 1996;Higgins 2000;Maxwell & Frinchaboy, in press). The present study raises the question of why variation in instar number exists in this species.…”

“…In arthropods, particularly important factors include immature growth and developmental rates, the number of nymphal instars, the duration of each instar, and genetic differences between the sexes and individuals (Higgins 1992(Higgins , 2000Higgins & rankin 1996;Fagan & Odell 1996;davidowitz et al 2004;Blanckenhorn 2000;Chown & Gaston 2010;González-Suárez et al 2011). In mantids, differences in food per capita among early instars affects body size and mass (Hurd & eisenberg 1984;Matsura et al 1984;Hurd & rathet 1986;Paradise & Stamp 1991;Fagan & Hurd 1994;dussé & Hurd 1997;Moran & Hurd 1997).…”