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Across vertebrates increased maternal investment (via increased pre- and
postnatal provisioning) is associated with larger relative brain size, yet
it remains unclear how brain organization is shaped by life history and
ecology. Here, we tested whether maternal investment and ecological
lifestyle are related to variation in brain size and organization across
100 chondrichthyans. We hypothesized that brain size and organization
would vary with level of maternal investment and habitat depth and
complexity. We found that chondrichthyan brain organization varies along
four main axes, according to: (1) absolute brain size, (2) relative
diencephalon and mesencephalon size, (3) relative telencephalon and
medulla size, and (4) relative cerebellum size. Increased maternal
investment is associated with larger relative brain size, while ecological
lifestyle is informative for variation between relative telencephalon and
medulla size, and relative cerebellum size after accounting for the
independent effects of reproductive mode. Deep-water chondrichthyans
generally provide low levels of yolk-only (lecithotrophic) maternal
investment and have relatively small brains, predominantly comprised of
medulla (a major portion of the hindbrain). Whereas, matrotrophic
chondrichthyans – which provide maternal provisioning beyond the initial
yolk-sac – found in coastal, reef, or shallow oceanic habitats have large
relative brain sizes, predominantly comprised of telencephalon (a major
portion of the forebrain). We demonstrated, for the first time, that both
ecological lifestyle and maternal investment are independently associated
with brain organization in a lineage with diverse life history strategies
and reproductive modes.
422 views reported since publication in 2019.