FNZ 57 - Apoidea (Insecta: Hymenoptera) - Evolutionary relationships
Donovan, BJ 2007. Apoidea (Insecta: Hymenoptera). Fauna of New Zealand 57, 295 pages.
(
ISSN 0111-5383 (print),
;
no.
57.
ISBN 978-0-478-09389-6 (print),
).
Published 07 Sep 2007
ZooBank: http://zoobank.org/References/B2070E05-13B6-4CBF-9A0A-0ACE40FA4796
Evolutionary relationships among endemic bees
Leioproctus (Leioproctus)
Morphologically there is little variation among the 11 species, apart from L. otautahi, and nothing to suggest which species, if any, may have given rise to the others. Indeed, the lack of morphological differentiation has led to a great deal of reliance on the differences in colour of various areas of the vestiture for species discrimination. The lack of morphological variation is particularly marked between males of L. boltoni, L. huakiwi, L. kanapuu, and L. metallicus, which makes identification of old males particularly difficult when vestiture is worn away. However, several features shared by one or more species are indicative of close relationships. The overall similarity between L. boltoni and L. kanapuu, apart from the lack of punctation of the clypeus of L. kanapuu, and the more restricted distribution of the latter, suggests it may have originated from L. boltoni. Some large females of L. pango from HB are very similar to small L. boltoni, which may be indicative of a recent divergence. The variation in the sculpturing of the propodeal triangle of females and the form of the apical lobes of the 7th metasomal sternum of male L. pango in different geographical regions suggests this widespread species may either already have diverged into several closely related cryptic species, or is in the process of doing so. The similarity of the ‘dented’ clypeus of female L. imitatus and L. metallicus, and the possession by both of white scopal hairs indicates a sister-group relationship between these 2 species; however, the facial vestiture of young males is quite different, with that of L. imitatus short, dense, and orange, but longer, not dense and white, in L. metallicus. Another sister group is that of L. purpureus and L. vestitus, which both possess a ‘bow wave’ appearance to their clypeal vestiture, and the overall structure of the clypeus with a median vertical ridge flanked by large punctures is common to both. On the other hand, the pygidial plates of L. metallicus and L. purpureus are both similarly very broad basally and irregularly ridged longitudinally, and that of L. vestitus less so, but these similarities may be due to their nesting in sand, where convergent evolutionary forces may have selected for a similar form best suited to the excavation of sand grains from tunnels of nests. The general appearance of the face of female L. keehua and L. waipounamu is similar, in that the clypeus of both is rather smoothly rounded from side to side, and is shiny, and for males the gonostyli of the genital capsule in dorsal and ventral views are similarly incurved. The restriction of L. keehua to saline estuarine habitats suggests a possible origin from the much more widespread L. waipounamu.
The single male L. otautahi fits into this subgenus using the key of Michener (2000), yet it possesses several characters not shared with the other 10 species, nor with the 7 species of L. (Nesocolletes). The light tessellation throughout the clypeus, the golden yellow-orange of the tegulae and wing veins out to about 1 tegular diameter (apart from a slight similarity in this character of some male L. vestitus), and the narrow, widely divergent apical lobes of the 7th metasomal sternum, are possibly sufficiently different to suggest L. otautahi should be placed in a third subgenus. The occurrence of just one specimen might suggests the bee originated in Australia and was found here through an incursion into New Zealand perhaps by shipping or aircraft, and perhaps from an as yet undescribed species in a new subgenus (see comments under species treatment). There is also a possibility that the specimen was collected in Australia and was incorrectly labelled. However the collector, E. S. Gourlay, was an entomologist of long-standing, so this seems unlikely. These issues cannot be resolved until further specimens become known, particularly females.
Leioproctus (Nesocolletes)
According to Michener (2000), L. (Nesocolletes) is unique to New Zealand, and is the only subgenus of the 32 subgenera with a long malar space, apart from the quite different South American L. (Torocolletes), which has 2 species. Michener (2000) states that L. (Nesocolletes) is related to Leioproctus proper, and more specifically to the metallicus group. He also says that some undescribed Australian species of Leioproctus sensu stricto also have elongate malar areas, but in other characters they are unlike both L. (Nesocolletes) and L. (Torocolletes). It is interesting that 1 male L. (Leioproctus) vestitus from Blue Stream, Tasman Valley, MK, has the malar space half as long again as normal, and 5 other males from the same site have the malar space twice as long as normal. This suggests quite some flexibility in this character even among New Zealand bees, so L. (Nesocolletes) could have originated from Australian or New Zealand L. (Leioproctus).
Three species of L. (Nesocolletes) are clearly closely related by overall similarities of morphology, and in particular by the unique very small size and quadrate form of the apical lobes of the 7th metasomal sternum of the males. These are: L. fulvescens, which is abundant over much of the South Island and is known from Stewart Island, L. nunui, of which only 6 specimens are known, all from the Awatere Valley, KA at the northern end of the South Island, and L. paahaumaa, which is common over the North Island. The overall orange-yellow vestiture of L. fulvescens is unique among all New Zealand Leioproctus, but interestingly L. paahaumaa shows a little of the same colour on the mesosoma, while much more is displayed on L. nunui. Another character indicative of a close similarity between L. fulvescens and L. paahaumaa is that both forage primarily on Asteraceae, and L. nunui has been captured both on Asteraceae and on Myrtaceae, although numbers are very small. The malar space of L. nunui is less than half as long as that of L. paahaumaa, which in turn is somewhat shorter than that of L. fulvescens. One interpretation of these factors is that L. fulvescens and L. paahaumaa evolved from a common ancestor, perhaps as a result of geographical separation after the formation of Cook Strait, and that L. nunui has evolved following an incursion of L. paahaumaa across Cook Strait into the northern end of the South Island. If this is true, then the more orange-yellow of the vestiture of L. nunui compared with that of L. paahaumaa may be due to whatever environmental factors that selected the orange-yellow of L. fulvescens acting similarly on L. nunui.
The short malar space of L. nunui, a species whose characters otherwise clearly categorise it in L. (Nesocolletes), indicates that the length of the malar space can be a flexible character of the subgenus. Thus L. maritimus which has a short malar space can, due to the possession of a declivous propodeal triangle, the possession of a well-developed metabasitarsal scopa, a peaked supraclypeus on females, and some development of a pseudopygidium in males, be regarded as a legitimate member of L. (Nesocolletes). Conversely, despite the lack of a metabasitibial scopa and the presence of an elongate rounded supraclypeus in females, the long malar space, declivous propodeal triangle, and in males an incipient pseudopygidium, place L. monticola in (Nesocolletes). However, there appear to be no obvious characters that might suggest the direction of evolutionary relationships between and/or among the 3 obviously related species discussed above and L. hudsoni, L. maritimus, L. monticola, and L. pekanui. On the other hand, the form of the apical lobes of the 7th metasomal sternum of the males of these 4 species is more like that of the males of L. (Leioproctus) (excluding L. otautahi) than are the very small apical lobes of L. fulvescens, L. nunui, and L. paahaumaa, which suggests that these latter 3 species are more derived than are the former 4 species.
Hylaeus (Prosopisteron)
On the basis of the form of the apex of the 8th metasomal sternum of males, the 6 endemic species can be divided into 2 groups: H. agilis and H. capitosus with the apex rounded, and H. kermadecensis, H. matamoko, H. murihiku, and H. relegatus with the apex bifid. Males of the first 2 species also are without any development of ridges or tubercles on metasomal sterna, whereas at least some specimens of all the species in the second group show some development of this character. In the second group, H. kermadecensis, which is restricted to the Kermadec Islands, generally appears to be quite similar to H. relegatus, which is widespread throughout the 3 main islands of New Zealand, and also the Chatham Islands and the Three Kings Islands. Possibly a dispersion event of an ancestral species followed by isolation of the bees on the Kermadec Islands has resulted in divergence into 2 species. The comparatively restricted distributions of H. matamoko and H. murihiku in the South Island may also indicate the isolation of parts of the same ancestral stock in different regions of the South Island.
However, the form of the apex of the 8th metasomal sternum of males, and the presence or absence of ridges or tubercles on metasomal sterna are not correlated; the adventive H. asperithorax has a bifid apex, but no ridges or tubercles, and H. perhumilis has a bifid apex, and sometimes paired tubercles. It is possible that ridges and/or tubercles are more a function of the size of males, rather than a character determined by genetics.
Lasioglossum (Austrevylaeus)
According to Dr K. L. Walker (pers. comm. March 2004), Australian and New Zealand species of Austrevylaeus share characters in common. This suggests the New Zealand species could have originated from more than 1 incursion of more than 1 species from Australia. However, L. sordidum is widespread and common over the 3 main islands and also 3 smaller islands, while L. mataroa and L. maunga are restricted, or are nearly restricted, to parts of the South Island, raising the possibility that these latter 2 species have originated from isolated populations of L. sordidum.