Mózg ptaków “mądrzeje” dokładnie tam, gdzie trzeba

Possible linkage between neuronal recruitment and flight distance in migratory birds

• Shay Barkan, Uri Roll, Yoram Yom-Tov, Leonard I. Wassenaar  & Anat Barnea

• Scientific Reports 6, Article number: 21983 (2016), doi:10.1038/srep21983

Introduction

Exposure to new information in adult animals has been positively correlated with the magnitude of new neuronal recruitment in their brains^1,2. This exposure, linked to new neuronal recruitment, could be manifested in many ways throughout an animal’s life history and the challenges it faces^3,4,5. The recruitment of new neurons is considered to be promoted by an elevated need to acquire new information in relevant brain regions⁶. Such recruitment may serve this purpose by facilitating brain plasticity and has been suggested to play an important role in acquiring new memories in both invertebrates^7,8 and vertebrates^1,9. Birds have been used as model animals in studies linking new neuronal recruitment with various behaviors, such as social complexity¹⁰, food hoarding^4,11, song learning¹², the reproductive cycle¹³, and others.

Long-distance migration is highly demanding in many aspects of a bird’s life cycle. Beyond the immense physiological effort required in traveling large geographical distances, birds also have to avoid predation, minimize resource competition, overcome adverse weather, and accurately navigate and orient¹⁴. The mortality rate of young avian migrants is far higher than that of their adult counterparts which suggests that learned experience is of great importance for migratory birds¹⁵. Indeed, several studies have explored the importance of learning and experience for accurate navigation in migratory birds^16,17. Learning could be key to improved navigation ability; identification of suitable stop-over sites en-route; avoidance of harsh weather or potential predators; and for outcompeting both fellow migrants and local birds. Such needs for increased learning ability during migration may be answered by a greater neuronal recruitment in the relevant brain regions of migratory birds. To date, only two studies of passerines^18,19 have directly investigated the possible relationship between neuronal recruitment and migratory behavior in birds. Those studies revealed that, for passerines, migrant species or sub-species possessed more new neurons than resident species in the brain regions that play a role in spatial information processing.

During the past century, great advances have been made in tracking and monitoring migratory birds. In addition to the increased use of recovery-based ringing and tagging, researchers nowadays have access to radio transmitters and satellite or GPS tracking to monitor individual birds²⁰. Recently, the use of stable isotopes has been shown to be effective in quantifying individual or population migratory connectivity^21,22. The use of stable isotopes to track migratory movement is based on the predictable global spatial patterns for hydrogen (H) and carbon (C) isotopes. Wherever a bird grows its feathers (often at its natal or overwintering site), the local isotopic patterns are translated through diet along the trophic cascade, and are fixed into the growing feathers, thereby reflecting the region the feathers were grown²³. When a bird is caught later, its feathers’ ²H/H and ¹³C/¹²C ratios can be non-lethally analyzed and compared to known H and C isotopic distribution base-maps (e.g. isoscapes). This tissue-to-isoscape comparison is used to obtain estimates of the region where a bird had molted or grown its feathers. One of the primary advantages of the isotope technique is that every bird captured provides intrinsic spatial information about its migration route, without the need for the mark-recapture used in ringing and marking techniques²⁴.

In this study we hypothesized a possible link between an increase in new neuronal recruitment and the distances traveled by migrant birds. We explored this phenomenon in reed warblers (Acrocephalus scirpaceus) and turtle doves (Streptopelia turtur), which are summer visitors in Israel and winter and molt in Africa²⁵. Migration distance estimates were determined using feather isotopic ratios as an indicator of molt locality in the wintering grounds. New neuronal recruitment was evaluated in two brain regions known to take part in navigation and spatial orientation tasks-the Hippocampal complex (HC)^26,27, and the nidopallium caudolateral (NCL)²⁷.

Czytaj więcej: http://www.nature.com/articles/srep21983

From: Possible linkage between neuronal recruitment and flight distance in migratory birds