Insect temperature–body size trends common to laboratory, latitudinal and seasonal gradients are not found across altitudes

Abstract

Body size affects rates of most biological and ecological processes, from individual performance to ecosystem function, and is fundamentally linked to organism fitness. Within species, size at maturity can vary systematically with environmental temperature in the laboratory and across seasons, as well as over latitudinal gradients. Recent meta‐analyses have revealed a close match in the magnitude and direction of these size gradients in various arthropod orders, suggesting that these size responses share common drivers. As with increasing latitude, temperature also decreases with increasing altitude. Although the general direction of body size clines along altitudinal gradients has been examined previously, to our knowledge altitude–body size (A–S) clines have never been synthesised quantitatively, nor compared with temperature–size (T–S) responses measured under controlled laboratory conditions. Here we quantitatively examine variation in intraspecific A–S clines among 121 insect species from 50 different global locations, representing 12 taxonomic orders. While some taxa were better represented in the literature than others, our analysis reveals extensive variation in the magnitude and direction of A–S clines. Following the assumption that temperature on average declines by 1°C per 150 m increase in altitude, order‐specific A–S clines in the field appear to deviate from laboratory T–S responses. Specifically, the magnitude of A–S clines and T–S responses are more closely matched in some taxonomic orders (e.g. Diptera) than others (e.g. Orthoptera). These findings contrast with the strong co‐variation observed between latitude‐size clines and T–S responses, and between laboratory and seasonal T–S responses. The lack of clear size relationships with elevation, and hence temperature, is likely due to the counteracting effects of other major drivers with altitude, including season length and oxygen partial pressure. Switches in voltinism within species across altitude, and the dispersal of individuals across different elevations, may also obscure trends. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13031/suppinfo is available for this article.

Altitudinal variation in life‐history traits in the lawn ground cricket, Polionemobius mikado

“…However, the head width was larger at 670 m than 800 m altitude, where the univoltine life cycle is expected to be maintained, as in other species of Orthoptera (Masaki ; Berner & Blanckenhorn ; Bidau & Martí ; Laiolo et al ; Eweleit & Reinhold ; Levy & Nufio ). Therefore, we conclude that the altitudinal variation in the head width was mainly resulted from the different lengths of the season available for growth, although lower temperature at higher altitudes might also be involved into the larger head width (Horne et al ). This altitudinal cline in the head width of P. mikado matches the expected pattern of the adult body size in insects that have variable voltinism (Roff ; Chown & Gaston ; Chown & Klok ).…”

Differences in Mobility and Dispersal Capacity Determine Body Size Clines in Two Common Alpine-Tundra Arthropods

“…Bowden et al [26] found that habitat heterogeneity at finer scales overrides effects at broader scales in species with low mobility. In turn, Hein et al [27] and Horne et al [28] recently proposed that high mobility in a species might obscure reactions to environmental factors at finer scales.…”

Moth body size increases with elevation along a complete tropical elevational gradient for two hyperdiverse clades

“…Poikilotherms, however, frequently display a positive relationship between ambient temperature and body size, with smaller body sizes in cooler climates and larger body sizes in warmer climates (a 'converse-Bergmann pattern'; Mousseau 1997). Investigations of a broad range of insect taxa, however, reveal no uniform geographical body size pattern for poikilotherms (Shelomi 2012, Zeuss et al 2017, Horne et al 2018, and suggest that processes controlling body size may be fundamentally different for poikilotherms than for homeotherms.…”