Mechanisms and Consequences of Partial Migration in Insects

Abstract

Partial migration, where a proportion of a population migrates, while other individuals remain resident, is widespread across most migratory lineages. However, the mechanisms driving individual differences in migratory tendency are still relatively poorly understood in most taxa, but may be influenced by morphological, physiological, and behavioral traits, controlled by phenotypic plasticity and the underlying genetic complex. Insects differ from vertebrates in that partial migration is often associated with pronounced morphological differences between migratory and resident phenotypes, such as wing presence or length. In contrast, the mechanisms influencing migratory tendency in wing-monomorphic insects is less clear. Insects are the most abundant and diverse group of terrestrial migrants, with trillions of animals moving across the globe annually, and understanding the drivers and extent of partial migration across populations will have considerable implications for ecosystem services, such as the management of pests and the conservation of threatened or beneficial species. Here, we present an overview of our current but incomplete knowledge of partial migration in insects. We discuss the factors that lead to the maintenance of partial migration within populations, and the conditions that may influence individual decision making, particularly in the context of individual fitness and reproductive tradeoffs. Finally, we highlight current gaps in knowledge and areas of future research that should prove fruitful in understanding the ecological and evolutionary drivers, and consequences of partial migration in insects.

A Review of the Phenotypic Traits Associated with Insect Dispersal Polymorphism, and Experimental Designs for Sorting out Resident and Disperser Phenotypes

“…Of note, partial migration, i.e., the migration of a portion of the population while the other part of the population remains resident, also exists in insects [52,53]. In a recent review on partial migration of insects, many of the examples used by the authors correspond to dispersal [54], an aspect that the authors recognized themselves ("Other movement ecology researchers might categorize some of the examples we provide in our review as dispersal instead of migration"); this suggests that the definition of migration in entomological studies is not yet clearly fixed.…”

A Review on Dispersal Polymorphism in Wing-Dimorphic, Mono-Morphic, Wingless, and Range-Expanding Insects, and Experimental Designs for Sorting out Resident and Disperser Phenotypes

“…the migration of a portion of the population while the other part of the population remains resident, also exists in insects [52][53]. In a recent review on partial migration of insects, many of the examples used by the authors correspond to dispersal [54], an aspect that the authors recognized themselves ('Other movement ecology researchers might categorize some of the examples we provide in our review as dispersal instead of migration'); this suggests that the definition of migration in entomological studies is not yet clearly fixed.…”

Quantifying flight aptitude variation in wildA. gambiaes.l. in order to identify long-distance migrants

“…Following conventional guidelines, the threshold for outlier detection were values > 3.5 MAD units from the median were considered as "High Flight Activity" (HFA), as opposed to "Low Flight Activity" (LFA) or short-range flight, which represented values < 3.5 MAD units. Unless a population is observed to be "on the move" as are migratory swarms of locusts (Kennedy, 1951) or monarch butterflies (Gibo and Pallett, 1979), it is generally assumed that at any moment the fraction of individuals that express migratory behavior is small (Dingle and Arora 1973;Taylor et al 1992;Taylor, Nault, and Styer 1993;Taylor et al 2010;Lee and Leskey 2015;Menz et al 2019). This assumption relies on Mark-Release-Recapture (MRR) studies suggesting that a sizeable proportion of the population remain near the area where they were marked, and also that the duration of the migratory phase last a few days and is typically shorter than the non-migratory phase, which can last several weeks or months (Johnson, 1969;Roff and Fairbairn, 2007).…”