Phenological, but not social, variation associated with climate differences in a eusocial sweat bee, Halictus ligatus, nesting in southern Ontario

Abstract

Studies of annual and geographic variation in eusocial bee populations suggest that more stringent environmental conditions result in stronger reproductive skew favouring queens, while moderate conditions favour increasing worker reproduction. To test these predictions, we compared the phenology and colony development of H. ligatus nesting in St. Catharines, Ontario, Canada to a previously studied aggregation 90 km north of St. Catharines, in Victoria, Ontario. Despite the close proximity of these two locations, St. Catharines has markedly shorter winters and longer summers. Comparisons between St. Catharines in 2006 and Victoria in the 1980s and 1990s incorporate both geographic differences in climate and temporal differences due to climate change. We predicted that St. Catharines foundress queens should emerge from hibernation and initiate nests earlier in spring, giving them time to produce more workers. Since earlier studies indicated that queens have difficulty suppressing worker reproduction in larger colonies, we also predicted higher rates of worker ovarian development in St. Catharines. In spring and summer 2006, we excavated 65 H. ligatus nests, comparing their contents to 713 specimens collected in pan traps. As predicted, nests were initiated about a month earlier in St. Catharines than in Victoria, but contrary to prediction, fewer workers were produced in St. Catharines. St. Catharines workers were just as likely to have developed ovaries as Victoria workers. About 40% of St. Catharines workers were classified as reproductive, and larger reproductive workers tended to have higher ovarian scores. RESEARCH ARTICLEMiriam H. Richards et al. / Journal of Hymenoptera Research 43: 19-44 (2015) 20 evidence that queens can initiate new nests following the loss of their first brood, overlap between worker and gyne production within some nests, and high rates of independent nest founding by worker-sized females, suggesting that many worker-brood females overwinter. Overall, the distinctly warmer climate of St. Catharines compared to Victoria led to earlier nest initiation and lengthening of the flight season, but not to the predicted differences in colony social organisation or queen-worker reproductive skew. A second objective of our study was to assess how well pan trap collections capture important information about demographic and social parameters important in assessing social variability in sweat bees. Nest excavations and pan traps produced similar results, suggesting that pan traps are a good alternative when nest excavations are impossible.

Nesting habits influence population genetic structure of a bee living in anthropogenic disturbance

“…On the other hand, climate change, which has already resulted in perceptibly earlier springs and longer summers in Ontario (Richards et al . ), could be promoting demographic expansion of populations at the northern edge of the range. Certainly, anecdotal evidence suggests that in Ontario, carpenter bees are much more numerous than they were previously, as it is only in recent decades that they have begun to be noticed by homeowners and pest control operators, despite their presence in the province for at least century (Skandalis et al .…”

Season length, body size, and social polymorphism: size clines but not saw tooth clines in sweat bees

“…Therefore, foundresses in solitary populations may provision less intensively than workers in social nests (Field, ; Richards, ; Neff, ). In addition, more southern social nests might contain more workers because foundresses emerge earlier (Plateaux‐Quénu, ; but see Richards et al ., ), more B1 females choose to work rather than enter hibernation (e.g. Yanega, ) or there are additional worker broods (Yanega, ; Strohm & Bordon‐Hauser, ).…”

“…Body size is strongly correlated with the amount and quality of food consumed during development (Plateaux-Quénu, 1983;Richards & Packer, 1994;Roulston & Cane, 2002). Thus, offspring size might also be influenced by environmental constraints on, and strategic investment decisions by, adult bees at the time of provisioning (Richards & Packer, 1996;Field et al, 2012;Richards et al, 2015).…”

Limited social plasticity in the socially polymorphic sweat bee Lasioglossum calceatum

“…Bees at Inverness nest solitarily but bees at Sussex typically express eusociality (Davison and Field 2016). Because nesting aggregations are hard to find (Richards et al 2015), we were unable to perform a control transplant from another eusocial site in the present study. However, controls implemented in previous studies show that transplantation per se is unlikely to influence behaviour (Field et al 2010, 2012; Davison and Field, in preparation).…”