Relating wing morphology and immune function to patterns of partial and differential bat migration using stable...

Area of Science:

• Zoology
• Ecology
• Physiology

Background:

• Migration is energetically costly, potentially leading to morphological and physiological trade-offs in migratory species.
• Wing morphology is often fixed, while immune defenses can be flexible, varying with energy availability.
• Silver-haired bats (Lasionycteris noctivagans) exhibit partial and differential migration patterns, making them ideal for studying these trade-offs.

Purpose of the Study:

• To investigate intraspecific variation in wing morphology and immune function in silver-haired bats based on migratory tendency and distance.
• To test the hypothesis that energy constraints of migration lead to specific adaptations in wing shape and immune response.
• To compare resident bats with short- and long-distance migrants.

Main Methods:

• Assessed wing morphology (e.g., size, shape, wing loading) and immune indices (e.g., IgG, neutrophil-to-lymphocyte ratio) in male silver-haired bats.
• Categorized bats into resident, short-distance northern migrant, long-distance northern migrant, and southern migrant groups.
• Used stable hydrogen isotope techniques to estimate breeding latitude of spring migrants.

Main Results:

• Long-distance northern migrants exhibited larger wings than short-distance migrants and lower wing loading than southern migrants.
• Short-distance northern migrants showed reduced IgG, while southern migrants had heightened neutrophils and neutrophil-to-lymphocyte ratios compared to residents.
• Body fat, aspect ratio, wing tip shape, and bacteria-killing ability did not significantly vary with migration status or distance.

Conclusions:

• Male silver-haired bats do not appear to substantially downregulate immune defenses or adopt specialized wing shapes for migration.
• Phenotypic changes related to migration costs might be more pronounced in female bats, which undertake longer migrations.
• Energetic costs of migration may be mitigated by behaviors like aerial hawking and heterothermy, reducing the need for significant morphological or physiological trade-offs.