Hybrid chickadees are deficient in learning and memory

Abstract

Identifying the phenotypes underlying postzygotic reproductive isolation is crucial for fully understanding the evolution and maintenance of species. One potential postzygotic isolating barrier that has rarely been examined is learning and memory ability in hybrids. Learning and memory are important fitness-related traits, especially in scatter-hoarding species, where accurate retrieval of hoarded food is vital for winter survival. Here, we test the hypothesis that learning and memory ability can act as a postzygotic isolating barrier by comparing these traits among two scatter-hoarding songbird species, black-capped (Poecile atricapillus) and Carolina chickadees (Poecile carolinensis), and their naturally occurring hybrids. In an outdoor aviary setting, we find that hybrid chickadees perform significantly worse on an associative learning spatial task and are worse at solving a novel problem compared to both parental species. Deficiencies in learning and memory abilities could therefore contribute to postzygotic reproductive isolation between chickadee species. Given the importance of learning and memory for fitness, our results suggest that these traits may play an important, but as yet overlooked, role in postzygotic reproductive isolation.

Multiple forms of selection shape reproductive isolation in a primate hybrid zone

“…Learning and memory have also been linked to postzygotic isolation since deficiencies in these traits can be selected against in hybrids (Rice & McQuillan, ). Recently, McQuillan, Roth, Huynh, and Rice () found that hybrid chickadees scored lower than parental chickadees in associative spatial learning and problem‐solving tasks. Learning and memory have been implicated in goal‐oriented foraging behaviour in Neotropical primates (Garber, ; Janson, ), traits presumably important for howler monkeys, which maintain a predominantly folivorous–frugivorous diet in highly diverse tropical forests where they adjust their dietary intake on seasonal availability of preferred foods (Raño, Kowalewski, Cerezo, & Garber, ).…”

Conspecific olfactory preferences and interspecific divergence in odor cues in a chickadee hybrid zone

“…We genotyped all birds at 10 species-diagnostic single nucleotide polymorphism markers (McQuillan et al, 2017). We ran STRUCTURE on this larger dataset of over 400 total genotypes using the same program settings as McQuillan et al (2017McQuillan et al ( , 2018 To do this, we combined the genotypes of our test subjects with a larger dataset from multiple Pennsylvania hybrid-zone populations, as well as known pure-species individuals from allopatric populations of both species (New York and Louisiana, USA).…”

“…However, postzygotic reproductive barriers are present. Hybrid chickadees also are less likely to solve novel problems (McQuillan et al, 2018). Additional costs to hybridization are also found in adult birds of mixed ancestry.…”

“…Additional costs to hybridization are also found in adult birds of mixed ancestry. Hybrid chickadees are compromised in their spatial memory ability (McQuillan, Roth, Huynh, & Rice, 2018), which is important for fitness in scatter-hoarding species such as chickadees (Sonnenberg, Branch, Pitera, Bridge, & Pravosudov, 2019). Hybrid chickadees also are less likely to solve novel problems (McQuillan et al, 2018).…”

“…Hybrid chickadees are compromised in their spatial memory ability (McQuillan, Roth, Huynh, & Rice, 2018), which is important for fitness in scatter-hoarding species such as chickadees (Sonnenberg, Branch, Pitera, Bridge, & Pravosudov, 2019). Hybrid chickadees also are less likely to solve novel problems (McQuillan et al, 2018). Taken together, the reduced hatching success of hybrid offspring combined with cognitive deficiencies in adult hybrids suggests there are severe costs to hybridization for chickadees in our eastern Pennsylvania hybrid zone populations.…”