Data from: Two-year bee, or not two-year bee? How voltinism is affected by temperature and season length in a high-elevation solitary bee

Organisms must often make developmental decisions without complete
information about future conditions. This uncertainty—for example, about
the duration of conditions favorable for growth—can favor bet-hedging
strategies. Here, we investigated the causes of life-cycle variation in
Osmia iridis, a bee exhibiting a possible bet-hedging strategy with
co-occurring one- and two-year life cycles. One-year bees reach adulthood
quickly but die if they fail to complete pupation before winter; two-year
bees adopt a low-risk, low-reward strategy of postponing pupation until
the second summer. We reared larval bees in incubators in various
experimental conditions and found that warmer—but not longer—summers, and
early birth dates, increased the frequency of one-year life cycles. Using
in situ temperature measurements and developmental trajectories of
laboratory- and field-reared bees, we estimated degree-days required to
reach adulthood in a single year. Local long-term (1950–2015) climate
records reveal that this heat requirement is met in only ~7% of summers,
suggesting that the observed distribution of life cycles is adaptive.
Warming summers will likely decrease average generation times in these
populations. Nevertheless, survival of bees attempting one-year life
cycles—particularly those developing from late-laid eggs—will be
<100%; consequently, we expect the life-cycle polymorphism to
persist.