Phenotype–environment mismatch errors enhance lifetime fitness in wild red squirrels

Abstract

Mismatches between an organism’s phenotype and its environment can result in short-term fitness costs. Here, we show that some phenotype – environment mismatch errors can be explained by asymmetrical costs of different types of errors in wild red squirrels. Mothers that mistakenly increased reproductive effort when signals of an upcoming food pulse were absent were more likely to correctly increase effort when a food pulse did occur. However, mothers that failed to increase effort when cues of an upcoming food pulse were present suffered lifetime fitness costs that could only be offset through food supplementation. In fluctuating environments, such phenotype – environment mismatches may therefore reflect a bias to overestimate environmental cues and avoid making the costliest error, ultimately enhancing lifetime fitness.

A future food boom rescues the negative effects of early-life adversity on adult lifespan in a small mammal

“…R. Soc. B 291: 20232681 was especially true when maternal reproductive output was mismatched to the food availability a squirrel would experience during the periods of weaning and independence [44]. For instance, juveniles were less likely to survive if they were born into a large litter in a non-mast year, likely due to increased competition with a greater number of siblings for both food and territories.…”

“…R. Soc. B 291: 20232681 squirrels in this region have co-evolved, and which alters behaviour, fitness, life histories and population dynamics at a large scale [43,44,60,61]. We experimentally replicated only one component of a food boom (e.g.…”

“…[73] elevated squirrel density relatively high number of squirrels living on study area (increased conspecific competition) [42,43,59,74] 1 year following peak in lynx-hare cycle a year characterized by a crash in hare density and expected prey-switching by lynx to red squirrels (increased likelihood of predation) [46] elevated mustelid density relatively high number of nest predators (increased likelihood of predation) [42,64] mean winter temperature relatively cold average winter temperatures (increased thermoregulatory costs) [42,48] large litter x non-mast year litter size mismatched to future food abundance (i.e. a large litter produced in a non-mast year when future food is low) [43,44] elevated squirrel density x later birth date relatively high number of squirrels living on study area and a later birth date (reduced likelihood of territory acquisition) [40,59,72] elevated squirrel density x slow postnatal growth relatively high number of squirrels living on study area and poorer growth (reduced likelihood of territory acquisition)…”

“…variable definition references a) potential sources of early-life adversity large litter size relatively large number of siblings born within the same litter (increased sibling competition for maternal resources and conspecific competition for territories) [48] later birth date date of birth is relatively late in the breeding season (increased conspecific competition for territories) [40,72] slow postnatal growth relatively low offspring growth rate during period of maternal dependence calculated as change in body mass from approximately 0 days to 25 days of age (reduced likelihood of territory acquisition) [40,44,59] non-mast year a year in which a white spruce mast does not occur (food scarcity)…”

A future food boom rescues the negative effects of cumulative early-life adversity on adult lifespan in a small mammal

“…This was especially true when maternal reproductive output was mismatched to future environmental conditions. For example, juveniles were less likely to survive if they were born into a large litter in a non-mast year in which future food production was low, likely as a result of increased sibling and conspecific competition for both food and territories (Petrullo et al . 2023).…”