Data from: Adaptation to hummingbird pollination is associated with reduced diversification in Penstemon

A striking characteristic of the Western North American flora is the
repeated evolution of hummingbird pollination from insect-pollinated
ancestors. This pattern has received extensive attention as an opportunity
to study repeated trait evolution as well as potential constraints on
evolutionary reversibility, with little attention focused on the impact of
these transitions on species diversification rates. Yet traits conferring
adaptation to divergent pollinators potentially impact speciation and
extinction rates, since pollinators facilitate plant reproduction and
specify mating patterns between flowering plants. Here we examine
macroevolutionary processes affecting floral pollination syndrome
diversity in the largest North American genus of flowering plants,
Penstemon. Within Penstemon, transitions from ancestral bee-adapted
flowers to hummingbird-adapted flowers have frequently occurred, although
hummingbird-adapted species are rare overall within the genus. We inferred
macroevolutionary transition and state-dependent diversification rates and
found that transitions from ancestral bee-adapted flowers to
hummingbird-adapted flowers are associated with reduced net
diversification rate, a finding based on an estimated 17 origins of
hummingbird pollination in our sample. While this finding is congruent
with hypotheses that hummingbird adaptation in North American Flora is
associated with reduced species diversification rates, it contrasts with
studies of neotropical plant families where hummingbird pollination has
been associated with increased species diversification. We further used
the estimated macroevolutionary rates to predict the expected pattern of
floral diversity within Penstemon over time, assuming stable
diversification and transition rates. Under these assumptions, we find
that hummingbird-adapted species are expected to remain rare, due to their
reduced diversification rates. In fact, current floral diversity in the
sampled Penstemon lineage, where less than one-fifth of species are
hummingbird-adapted, is consistent with predicted levels of diversity
under stable macroevolutionary rates.