Brain Size and Morphology of the Brood-Parasitic and Cerophagous Honeyguides (Aves: Piciformes)

Abstract

Honeyguides (Indicatoridae, Piciformes) are unique among birds in several respects. All subsist primarily on wax, are obligatory brood parasites and one species engages in ‘guiding' behavior in which it leads human honey hunters to bees' nests. This unique life history has likely shaped the evolution of their brain size and morphology. Here, we test that hypothesis using comparative data on relative brain and brain region size of honeyguides and their relatives: woodpeckers, barbets and toucans. Honeyguides have significantly smaller relative brain volumes than all other piciform taxa. Volumetric measurements of the brain indicate that honeyguides have a significantly larger cerebellum and hippocampal formation (HF) than woodpeckers, the sister clade of the honeyguides, although the HF enlargement was not significant across all of our analyses. Cluster analyses also revealed that the overall composition of the brain and telencephalon differs greatly between honeyguides and woodpeckers. The relatively smaller brains of the honeyguides may be a consequence of brood parasitism and cerophagy (‘wax eating'), both of which place energetic constraints on brain development and maintenance. The inconclusive results of our analyses of relative HF volume highlight some of the problems associated with comparative studies of the HF that require further study.

Evidence for adaptive brain tissue reduction in obligate social parasites (Polyergus mexicanus) relative to their hosts (Formica fusca)

“…The possibility of brain reduction in social parasites has been explored in birds. The evolution of brood parasitism in birds was associated with reduced brain size in several clades, but the adaptive reasons for this pattern are not clear (Boerner & Kruger, ; Corfield et al ., ). Slave‐makers and their hosts are well suited to comparative analysis because slave‐makers are closely phylogenetically related to their hosts (Brady et al ., ; Moreau et al ., ; Buschinger, ).…”

Anatomical Specializations for Enhanced Olfactory Sensitivity in Kiwi, <b><i>Apteryx mantelli</i></b>

“…Data were compiled from the studies of Ebinger and Lohmer [1984], Corfield et al [2012b], Boire [1989], Cunningham et al [2013], Pistone et al [2002], Rehkamper et al [1991], Carezzano and Bee De Speroni [1995], Mehlhorn et al [2010], Fernandez et al [1997], and Alma and Bee De Speroni [1992]. Additional data on olfactory bulb size in California quail (Callipepla californica), black-winged stilt (Himantopus himantopus), South Island oystercatcher (Haematopus finschi), ostrich (S. camelus), and red-winged tinamou (R. rufescens) were obtained from the same specimens used in the studies of Cunningham et al [2013] and Corfield et al [2012c].…”

“…It is likely that all regions of a brain will shrink by the same amount, and therefore comparison of relative brain sizes reduces the amount of error when combining data from multiple studies [Corfield et al, 2012c]. Indeed, when comparing, for example, the size of the brain and the olfactory bulb in pigeons between the studies of Ebinger and Lohmer [1984] and Corfield et al [2012b], we found some differences in the sizes of both structures but the percentage of the telencephalon occupied by the olfactory bulb was nearly identical ( table 1 ).…”

The Central Nervous System of Jawless Vertebrates: Encephalization in Lampreys and Hagfishes

“…However, there is also considerable residual variation in brain size around these allometric lines within and across various vertebrate groups, implying that brain size also depends on a nonsomatic component, which has been associated with a range of life history traits, such as parental investment, primary habitat, and feeding mode [Lefebvre et al, 2004;Yopak and Frank, 2009;Mull et al, 2011;Swanson et al, 2012;Corfield et al, 2013;Willemet, 2013;Tsuboi et al, 2015]. Previous studies on the allometric relationship between brain and body size have focused primarily on the gnathostomes, and thus relatively little is known about brain scaling in agnathans.…”