A possible relation between new neuronal recruitment and migratory behavior in Acrocephalus warblers

Abstract

Evidence suggests a possible correlation between learning abilities of adults and new neuronal recruitment into their brains. The hypothesis is that this brain plasticity enables animals to adapt to environmental changes. We examined whether there are differences in neuronal recruitment between resident and migrant birds. We predicted that migrants, which are more exposed to spatial changes than residents, will recruit more new neurons. To test this, we compared neuronal recruitment in two closely related bird species - the migrant reed warbler (Acrocephalus scirpaceus), and the resident Clamorous warbler (A. Stentoreus) - during spring, summer, and autumn. Wild birds were caught, treated with BrdU and sacrificed five weeks later. New neurons were recorded in the Hippocampus and Nidopallium caudolateral. The results support our hypothesis, as more new neurons were found in the migrant species, in both brain regions and all seasons. We suggest that this phenomenon enables enhanced navigational abilities, which are required for the migratory lifestyle. However, in contrast to our hypothesis, in spring we found less new neurons in adults of both species, as compared to other seasons. We suggest that in spring, when birds settle in breeding territories, they require less spatial skills, and this might enable to reduce the cost of neuronal recruitment, as reflected by less new neurons in their brains. We also found age differences, with overall higher neuronal recruitment in juveniles. Finally, we advocate the importance of studying wild populations, for a better understanding of the adaptive significance of neuronal replacement in the vertebrate brain.

Exploring the Relationship between Brain Plasticity, Migratory Lifestyle, and Social Structure in Birds

“…In both species we recorded, in spring, summer, and autumn, the number of new neurons in the three brain regions that are thought to be relevant for the processing of spatial information—the HA, HC, and NCL. We hypothesized that, similar to our previous findings in passerines (Barkan et al, 2014), new neuronal recruitment in these brain regions would be higher in the migrant turtle dove than in the resident laughing dove, and that this pattern will correlate with the migration seasons.…”

“…The roles of the HC and NCL in processing spatial information were described in our previous study (Barkan et al, 2014; and see also the recent review by Herold et al, 2015). The third brain region, HA, is part of the Wulst, a brain region considered to be homologous to the mammalian visual cortex, although some of its structures evolved independently in birds and mammals (Medina and Reiner, 2000).…”

“…Accordingly, we aimed to extend our previous study (Barkan et al, 2014) and investigate whether the positive correlation that we had found in passerines, between migratory lifestyle and neuronal recruitment, exists also in non-passerine species. If so, we hypothesized that, as in passerines, new neuronal recruitment into relevant brain regions will be more pronounced in migrant species that travel long-distances twice a year, than in resident ones.…”

“…For example, LaDage et al (2011) showed that migratory adult white-crowned sparrows ( Zonotrichia leucophrys gambelii ) recruit more new hippocampal neurons than their residential subspecies ( Z. l. nuttalli ). More recently, we extended this examination (Barkan et al, 2014), looking at two brain regions known to be involved in processing spatial information—the hippocampus (HC) and the nidopallium caudolaterale (NCL), and compared new neuronal recruitment in these regions between two closely-related species—the migratory reed warbler ( Acrocephalus scirpaceus ) and the residential clamorous warbler ( A. stentoreus ). Similarly to LaDage et al (2011), our study, which was carried out under semi-natural conditions, found more new neurons in both the HC and NCL of the migrant species, compared to the resident one.…”

Factors That Modulate Neurogenesis: A Top-Down Approach

“…In support of cognitive maps used in migratory animals, migratory birds have been shown to have better spatial memory recall as well as increased hippocampal neurogenesis compared to nonmigratory birds [e.g. Healy et al, 1996;Cristol et al, 2003;Mettke-Hoffmann and Gwinner, 2003;Pravosudov et al, 2006;LaDage et al, 2011;Barken et al, 2014]. Similarly, changes in migratory status across the year have been shown to influence the production of new neurons, likely due to differential demands on spatial processing throughout the season.…”