Body size but not colony size increases with altitude in the holarctic ant, Leptothorax acervorum

Abstract

1. Bergmann's rule states that organisms inhabiting colder environments show an increase in body size or mass in comparison to their conspecifics living in warmer climates. Although originally proposed for homoeothermic vertebrates, this rule was later extended to ectotherms. In social insects, only a few studies have tested this rule and the results were ambiguous. Here, ‘body size’ can be considered at two different levels (the size of the individual workers or the size of the colony). 2. In this study, data from 53 nests collected along altitudinal gradients in the Alps were used to test the hypotheses that the worker body size and colony size of the ant Leptothorax acervorum increase with increasing altitude and therefore follow Bergmann's rule. 3. The results show that the body size of workers but not the colony size increases with altitude. Whether this pattern is driven by starvation resistance or other mechanisms remains to be investigated.

Does social thermal regulation constrain individual thermal tolerance in an ant species?

“…However, our results highlight that worker size differs dramatically with elevation. A similar result was obtained by Bernadou, Römermann, Gratiashvili, and Heinze (2016), who studied Leptothorax acervorum populations along an elevational gradient in the Alps. It is not known whether these size differences are genetically determined, or whether they result from phenotypic plasticity.…”

Habitat disturbance selects against both small and large species across varying climates

“…For ants, the relationship between the body size of workers and latitude or elevation has been examined in several previous studies, with four showing a negative size-temperature relationship (intraspecific: Heinze and Oberstadt 1999, Heinze et al 2003, Bernadou et al 2016) (interspecific: Cushman et al 1993, three showing no pattern (interspecific: Gomez and Espadaler 2000, Geraghty et al 2007, myrmecochores only: Gomez and Espadaler 2013, and one showing the converse relationship (intraspecific: Diniz and Fowler 1998). Studies examining the colony size of ants and other social insects have been similarly inconsistent (intraspecific: Bernadou et al 2016, interspecific: Kaspari and Vargo 1995, Porter and Hawkins 2001, Geraghty et al 2007). However, it is notable that those operating at the largest spatial and taxonomic scales (Cushman et al 1993, Kaspari andVargo 1995 andthis study) are consistent in showing a negative temperature-size relationship among species.…”

DraftAphaenogastergenomes expand our view of ant genome size variation across climate gradients

“…There is evidence of cold selecting for greater body size (i.e. Bergmann’s Rule) in ants (Heinze et al, 2003; Bernadou et al, 2016), and some have hypothesized that increased body size could lead indirectly to increased genome size via increased cell size (Ryan Gregory, 2005); however, the most recent, broad analysis of genome size in ants (that we are aware of) did not find support for a relationship between ant genome size and body size after controlling for phylogenetic patterns (Tsutsui et al, 2008). Therefore, assuming that our analysis adequately controlled for phylogenetics, indirect selection on genome size via body size is not a likely explanation for our observed relationship between genome size and temperature.…”