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Morphological caste differences in the neotropical swarm‐founding and polygynous polistine wasp, Polybia Scutellaris

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Page 1: Morphological caste differences in the neotropical swarm‐founding and polygynous polistine wasp, Polybia Scutellaris

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Page 2: Morphological caste differences in the neotropical swarm‐founding and polygynous polistine wasp, Polybia Scutellaris
Page 3: Morphological caste differences in the neotropical swarm‐founding and polygynous polistine wasp, Polybia Scutellaris
Page 4: Morphological caste differences in the neotropical swarm‐founding and polygynous polistine wasp, Polybia Scutellaris
Page 5: Morphological caste differences in the neotropical swarm‐founding and polygynous polistine wasp, Polybia Scutellaris
Page 6: Morphological caste differences in the neotropical swarm‐founding and polygynous polistine wasp, Polybia Scutellaris
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Page 9: Morphological caste differences in the neotropical swarm‐founding and polygynous polistine wasp, Polybia Scutellaris

369Caste differences in polistine wasps

A. multipicta

Among the mean relationships of the 22 analysed characters (Table 2, Fig. 4),17 of them show queen/worker ratios higher than 1.00. In contrast, only four char-acters, primarily of the head plus hamuli number (NH) and metanotum length(MNL), showed queen/worker ratios lower than 1.00. Only the maximum interorbi-tal distance (IDx) was equal to 1.00. Among the measured characters, metanotumlength (MNL) and the maximum interorbital distance (IDx) did not differ signifi-cantly between castes (t-test, P < 0.05). This indicates that queens are larger thanworkers except in five characters (HW, IDx, EW, NH, MNL).

The result of the canonical discriminant analysis based on 22 charactersstrengthens the clear dimorphism between inseminated egg-layers (queens) anduninseminated sterile females (workers). Queens showed higher values of the firstcanonical variate (CAN1) than workers (1.0 to 9.0 vs –7 to –1) (Fig. 6). To calculatethe CAN1 the following equation was used:

CAN1 = -20.19(HW-2.63)-0.57(HL-2.31)-8.37(IDx-2.25)+13.51(IDm-1.20)+1.41(GW-0.62)+1.41(EW-0.62)+1.75(MSL-1.80)+3.79(MSW-1.87)+9.08(PW-2.28)+5.66(MTL-0.66)-0.82(MNL-0.54)-2.71(MSH-2.76)+1.09(AL-4.25)+2.93(PL-1.28)+1.98(T1L-2.31)+3.04(T1BH-0.48)+6.12(T1AH-0.83)+0.79(T2L-2.16)+7.61(T2BW-1.19)+2.20(T2AW-2.57)-0.93(WL-5.92)-0.62(NH-0.36).

For determining CAN1 (Table 1), basal width of tergite II (T2BW), head width(HW) and, especially, pronotum width (PW) were the most important among theexamined characters. The Mahalanobis distance (D2, ANDERSON 1958) calculated

Fig. 6. — Discrimination between queens and workers of Agelaia multipicta multipicta based on thecanonical discriminant analysis using 21 metric characters and the number of hamuli. The equationto calculate the first canonical variate (CAN1) is shown in the text.

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370 F.B. Noll, D. Simões and R. Zucchi

through the CDA was 110.99 between queens and workers. In addition some mor-phological queen-worker differences were shown: (1) petiole larger with more hairsin queens, (2) queen’s gaster larger and paler than workers, (3) worker’s middletibia brown but yellow in queens, (4) interspace between antennal insertion brown-ish in workers but yellow in queens.

DISCUSSION

Three patterns of caste differentiation have been recognized for epiponinewasps according to RICHARDS (1978): (1) conspicuous size and allometric differenc-es present, with queens larger than workers in the absence of intermediates (A.areata, JEANNE & FAGEN 1974; A. vicina, SAKAGAMI et al. 1996; Protonectarina sylvei-rae, SHIMA et al. 1996b); (2) conspicuous dimorphism present, with queens smallerthan workers and no intermediates present (Apoica flavissima, SHIMA et al. 1994;Polybia dimidiata, SHIMA et al. 1996a); (3) morphological differences slight or indis-tinct, and intermediates present (Pseudopolybia vespiceps, S.N. SHIMA et al. in prep.;Protopolybia exigua, NOLL et al. 1997). However, in some groups, queens are signifi-cantly smaller than workers in some characters and larger in others. According toJEANNE et al. (1995), in Apoica pallens this is considered as non-size-based allome-try probably due to a reprogramming in growth parameters (WHEELER 1991). Sucha pattern was detected also in Epipona guerini (HUNT et al. 1996), Pseudopolybia dif-ficilis (JEANNE 1996), Apoica flavissima (SHIMA et al. 1994), and Polybia dimidiata(SHIMA et al. 1996a).

Queen-worker dimorphism in A. multipicta and A. pallipes is similar to otherAgelaia previously analysed, that is, queens are larger than workers with no inter-mediates present. In addition, colour and morphological differences were alsodetected. In A. multipicta, CAN1 values of queens and workers displayed a widerrange than those of A. pallipes. Although these two species are morphologically verysimilar (RICHARDS 1978), among the four most discriminant characters observed,only head width (HW) applies to both species, although most of the other charac-ters are gaster related. The finding that queen-worker mean ratios are not signifi-cantly different in two characters (IDx and MNL), for A. multipicta and for onlyone (NH), for A. pallipes, indicates that queens are larger than workers in practical-ly all the analysed characters.

The Mahalanobis distances obtained for A. pallipes and A. multipicta (124.67and 110.99, respectively) are considered high if compared with A. vicina (176.7,F.B. NOLL et al. in prep.). Species from other genera show lower values of Mahalan-obis distances: Pseudopolybia vespiceps (0.99, S.N. SHIMA et al. in prep.), Polybiadimidiata (6.76, SHIMA et al. 1996a), Protonectarina sylveirae (8.64, SHIMA et al.1996b), Protopolybia exigua (4.95, NOLL et al. 1997), Parachartergus smithii (10.31,S. MATEUS et al. in prep.) and Apoica flavissima (11.27, SHIMA et al. 1994).

As previously expected, A. pallipes and A. multipicta demonstrated the largestcaste dimorphism among the species studied in our serial work. These two speciesdiffer from Apoica flavissima (SHIMA et al. 1994) and Polybia dimidiata (SHIMA et al.1996a), in that queens are larger than workers, which is comparable to Protonecta-rina sylveirae but much more pronounced. Except for Agelaia lobipleura (RICHARDS

1978), marked queen/worker dimorphism has been reported in other Agelaia spp.(A. flavipennis, EVANS & WEST-EBERHARD 1970; A. areata, JEANNE & FAGEN 1974; A.

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371Caste differences in polistine wasps

vicina, VON IHERING 1903, SAKAGAMI et al. 1996), indicating that well-developed castedifferentiation is widely distributed in this taxon as suggested by RICHARDS (1978).Although the same pattern of caste differentiation is observed, A. vicina and A. fla-vipennis have larger queens than A. pallipes and A. multipicta, especially the gasterrelated characters (Fig. 4). This conclusion is reinforced by the queen/workerdimorphism based on the alitrunk length: 1.08 for A. pallipes and A. multipicta,1.12 for A. vicina (F.B. NOLL et al. in prep.), 1.12-1.16 for A. areata (JEANNE & FAGEN

1974) and 1.10 for A. flavipennis (F.B. NOLL unpub.). These values can be consid-ered because in vespines queen/worker dimorphism based on the thorax width wasestimated in 1.37 and 1.34 for Vespula germanica and V. rufa, respectively (BLACKITH

1958). In relation to ovary development, A. pallipes and A. multipicta are closely

related to Apoica flavissima (SHIMA et al. 1994) and Protonectarina sylveirae (SHIMA

et al. 1996b), in which only the queens were inseminated and had well-developedovaries, unlike workers which have the opposite conditions and, in addition, inter-mediates were absent.

ACKNOWLEDGMENTS

This study was supported by grants from Fundação de Amparo à Pesquisa do Estado deSão Paulo (FAPESP). The identification of Agelaia multipicta multipicta and Agelaia pallipespallipes was confirmed by the late Professor O.W. Richards. Special thanks to Professor Wil-liam D. Hamilton for offering the specimens (one worker and one queen) of Agelaia flavipen-nis analysed. This paper was improved due to the comments of three anonymous refereesand, especially those of Dr John Wenzel.

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