Hippocampal neurogenesis and volume in migrating and wintering semipalmated sandpipers (Calidris pusilla)

Abstract

Long distance migratory birds find their way by sensing and integrating information from a large number of cues in their environment. These cues are essential to navigate over thousands of kilometers and reach the same breeding, stopover, and wintering sites every year. The semipalmated sandpiper (Calidris pusilla) is a long-distance migrant that breeds in the arctic tundra of Canada and Alaska and winters on the northeast coast of South America. Its fall migration includes a 5,300-kilometer nonstop flight over the Atlantic Ocean. The avian hippocampus has been proposed to play a central role in the integration of multisensory spatial information for navigation. Hippocampal neurogenesis may contribute to hippocampal function and a variety of factors including cognitive activity, exercise, enrichment, diet and stress influence neurogenesis in the hippocampus. We quantified hippocampal neurogenesis and volume in adult migrating and wintering semipalmated sandpipers using stereological counts of doublecortin (DCX) immunolabeled immature neurons. We found that birds captured in the coastal region of Bragança, Brazil during the wintering period had more DCX positive neurons and larger volume in the hippocampus than individuals captured in the Bay of Fundy, Canada during fall migration. We also estimate the number of NeuN immunolabeled cells in migrating and wintering birds and found no significant differences between them. These findings suggest that, at this time window, neurogenesis just replaced neurons that might be lost during the transatlantic flight. Our findings also show that in active fall migrating birds, a lower level of adult hippocampal neurogenesis is associated with a smaller hippocampal formation. High levels of adult hippocampal neurogenesis and a larger hippocampal formation found in wintering birds may be late occurring effects of long distance migratory flight or the result of conditions the birds experienced while wintering.

Hippocampal Astrocytes in Migrating and Wintering Semipalmated Sandpiper Calidris pusilla

“…It is important to note that in previous work we detected an increase in volume in wintering C. pusilla when compared to migrating ( de Morais Magalhães et al, 2017 ). In the present results this reduction in volume of hippocampal formation was not detected, suggesting that other cells of the hippocampal formation and associated neuropil may have effect over the volume and more data is necessary to clarify what generates the observed volume fluctuation.…”

“…Because we have no information in the literature about potential influence of sex and age on hippocampal astrocytes morphology in long-distance migratory birds, and we did not measure the age of individuals in our sample due to technical limitations, it is difficult to discuss these potential influences in detail. However, experience and sex are important variables that have been previously demonstrated to influence hippocampal-dependent tasks in birds ( Astié et al, 2015 ; Rensel et al, 2015 ; Guigueno et al, 2016 ; Bingman and MacDougall-Shackleton, 2017 ), and migratory behavior is accompanied by hippocampal morphological changes including volume and neurogenesis ( Barkan et al, 2016 , 2017 ; de Morais Magalhães et al, 2017 ). Thus, these variables should be considered in future studies of hippocampal astrocytes morphologies in long-distance migratory birds.…”

“…et al, 2016 ). In addition, de Morais Magalhães et al (2017) demonstrated that the long-distance migratory species Calidris pusilla has a significant difference in the number of newborn neurons in migrating and wintering individuals. However, most studies of the role of the hippocampal plastic response in memory formation have focused on the number of neurons and on changes in hippocampal volume, with few reports investigating the role of glial cells and the hippocampus in migration ( Healy et al, 1996 ; Roth et al, 2013 ).…”

Adult Hippocampal Neurogenesis in Different Taxonomic Groups: Possible Functional Similarities and Striking Controversies

“…The generation of neurons in the adult bird brain was demonstrated in the ventricular hyperestriatum using [H 3 ]-thymidine [4]. Since then, several studies have revealed the existence of adult neurogenesis as a well-established and widespread phenomenon in birds [82,83,84,85,86].…”

“…The generation and survival of new neurons is influenced by several life-related factors, such as food restriction [94], seasonality [95], migratory experiences [86], migratory distance [96], and learning and memory [97,98].…”