Breaking Haller's rule: brain-body size isometry in a minute parasitic wasp.
Throughout the animal kingdom, Haller's rule holds that smaller individuals have larger brains relative to their body than larger-bodied individuals. Such brain-body size allometry is documented for all animals studied to date, ranging from small ants to the largest mammals. However, through experimental induction of natural variation in body size, and 3-D reconstruction of brain and body volume, we here show an isometric brain-body size relationship in adults of one of the smallest insect species on Earth, the parasitic wasp Trichogramma evanescens. The relative brain volume constitutes on average 8.2% of the total body volume. Brain-body size isometry may be typical for the smallest species with a rich behavioural and cognitive repertoire: a further increase in expensive brain tissue relative to body size would be too costly in terms of energy expenditure. This novel brain scaling strategy suggests a hitherto unknown flexibility in neuronal architecture and brain modularity.
Laboratory of Entomology, Wageningen University, Wageningen, The Netherlands. emma.vanderwoude@wur.nl
Emma
E
van der Woude
Hans M
HM
Smid
Lars
L
Chittka
Martinus E
ME
Huigens
D000818:Animals; D049628:Body Size / Q000235:genetics; D001921:Brain / Q000033:anatomy & histology*; D005838:Genotype; D018613:Microscopy, Confocal; D009929:Organ Size; D014863:Wasps / Q000033:anatomy & histology* / Q000235:genetics