Hymenoptera, Apidae, Meliponini)*,**
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Apidologie 37 (2006) 653–664 653 c INRA/DIB-AGIB/ EDP Sciences, 2006 DOI: 10.1051/apido:2006046 Original article Size variation and egg laying performance in Plebeia remota queens (Hymenoptera, Apidae, Meliponini)*,** Márcia de Fátima R, Pérsio de Souza S-F, Vera Lúcia I-F Laboratório de Abelhas, Depto. de Ecologia, Instituto de Biociências, Universidade de São Paulo, R. do Matão, trav. 14, n. 321, 05508-900 São Paulo, SP, Brazil Received 2 September 2005 – Revised 2 January 2006 – Accepted 9 January 2006 Abstract – Stingless bees may produce both large queens and "miniature" queens, but the adaptive signifi- cance of this is uncertain. Using biometry and statistical analysis we determined the proportion of miniature queens in Plebeia remota that were either mated (14%) or virgin (45%). Mated queens were mostly normal- sized which indicated that they were more successful. Nevertheless, the presence of miniature mated queens heading colonies confirmed that they also are viable. The egg-laying capacity of mated queens of differ- ent sizes was determined using colony exchange experiments. The results showed that egg laying is not influenced by size differences. Therefore, miniature mated queens may be as successful in laying eggs as normal-sized queens. Finally we discuss some ultimate hypotheses for why miniature queens are produced. queen size variation / miniature queen / egg laying / stingless bee / Plebeia remota 1. INTRODUCTION in some trigonine species, virgin queens may occasionally also be reared from worker-sized Stingless bees show a variety of ways in cells, as in Melipona (Imperatriz-Fonseca which queens are reared. Trophic aspects are et al., 1997). Moreover, in Leurotrigona muel- extremely important for caste determination, leri and Frieseomelitta varia queens may be although genetic factors also seem to play a produced in a special way. The cells of the role (at least for Melipona species; for a review comb are arranged in clusters and when two see Velthuis and Sommeijer, 1991). cells are contiguous a larva also may eat the There are two main methods of rearing contents of the neighbouring cell. After that queens. In the genus Melipona virgin queens the workers transform the cell into a royal emerge from cells that are of the same size cell (Terada, 1974; Faustino et al., 2002). The as those used to rear workers and males. In queens produced from normal-sized cells are contrast, in Trigona and related genera,virgin smaller than the ones reared from royal cells, queens are generally produced from larger, and are referred to as miniature or dwarf specially constructed royal cells. Nevertheless, queens (Engels and Imperatriz-Fonseca, 1990; Imperatriz-Fonseca and Zucchi, 1995). Conse- Corresponding author: M. de F. Ribeiro, quently, these species produce queens of two [email protected] sizes: miniature and normal-sized queens. Present address: Depto. de Zootecnia, Universidade Federal do Ceará – UFC, Bloco 809 Campus do So far, miniature queens have been PICI, 60021-970 Fortaleza, CE, Brazil. observed in six species: Cephalotrigona * Manuscript editor: Gudrun Koeniger femorata (Nogueira Neto, 1951), Ple- ** The present manuscript preceded the Review ar- beia juliani (Juliani, 1962), Schwarziana ticle published in Apidologie 37, 191–206, 2006. quadripunctata (Camargo, 1974; Imperatriz- Article published by EDP Sciences and available at http://www.edpsciences.org/apido or http://dx.doi.org/10.1051/apido:2006046 654 M.F. Ribeiro et al. Fonseca and Darakjian, 1993, Nogueira- collected 112 virgin queens and 71 mated queens Ferreira et al., 2000), Plebeia remota which were heading colonies. Virgin queens were (Imperatriz-Fonseca et al., 1975), P. emerina mostly collected from chambers where they may (A.M.P. Kleinert personal comm.), and Nan- be kept for a variable period of time (Imperatriz- notrigona testaceicornis (Imperatriz-Fonseca Fonseca and Zucchi, 1995). The following mor- et al., 1997). In most of these species, the phometric measurements were taken from each in- production of miniature queens is considered dividual using a stereomicroscope fitted with an a rare phenomenon. In S. quadripunctata, ocular micrometer (12 xs): head width (HEAD), however, miniature queen production can medium interorbital distance (IOD), and intertegu- reach high levels (Camargo, 1974; Imperatriz- lar distance (ITEG). All measurements were taken non-invasively from live bees using an apparatus Fonseca and Zucchi, 1995), with as many described in Ribeiro and Alves (2001). as 86% of all queens reared being miniature (Wenseleers et al., 2005). A large number The size of virgin and mated queens was com- of miniature queens were also found to be pared using nonparametric Mann-Whitney U test, reared in P. re mo ta (Ribeiro et al., 2003a). since HEAD, IOD, and ITEG were not normally distributed (Kolmogorov-Smirnov test, mod. Lil- For the other species, no information on liefors, see Results). the production of miniature virgin queens is available. To distinguish miniature and normal-sized Most virgin queens are killed by work- queens based on our biometrical measurements we ers soon after emergence. Those that sur- developed the following analytical protocol. First, vive may swarm with some workers to start we established that there was bimodality by show- ing that the size distributions were not normally a new colony, or replace the old queen. distributed, characterised by a test for normality Therefore, only a small percentage of virgin ff through usual statistical tests; absence of normal- queens become e ective queens (Engels and ity indirectly indicates non-unimodality. Second, Imperatriz-Fonseca, 1990; Imperatriz-Fonseca we tested for kurtosis of the distributions against and Zucchi, 1995). Except for S. quadripunc- that expected under normal distribution; a signifi- tata (Ribeiro and Alves, 2001; Wenseleers cant negative kurtosis is an indicator of bimodal- et al., 2005) it has not been reported whether a ity (Wyszomirski, 1992). Once these two steps were miniature gyne may supersede a normal-sized applied and sufficient evidence for bimodality was mother-queen, mate and lay eggs normally. found, we performed a third step, a k-means clus- The aim of this study was to compare tering using Euclidean distances based on near- the performance of miniature and normal- est centroid sorting (Anderberg, 1973), with two sized queens in P. re mo ta .Todothis,we a priori groups (i.e. K = 2, normal sized and minia- first compared the proportion of virgin and ture queens) including all three variables previously mated queens that were miniature. We clas- found to be bimodal, and using iterative estimation sified queens by using detailed morphometry of cluster centroids. As a final check on the efficacy and discriminant analysis. Second, we com- of the discrimination of morphotypes, a discrimi- pared egg laying performance of miniature and nant analysis was applied as a fourth step using the normal-sized queens using colony exchange cluster membership as the classification variable. experiments. Finally, we also discussed some The degree of correct allocation of individuals to evolutionary hypotheses as to why miniature morphotypes was assessed through jackknife cross validation, and by examining the between-groups queens are produced. to within-groups variability with Wilk’s lambda. Equality of group covariance matrices and multi- 2. MATERIALS AND METHODS normality were tested by the omnibus Box’s M test. In addition, a Principal Components Analysis 2.1. Size variation (PCA) using the three bimodal variables (HEAD, IOD, ITEG) was made, and the first principal com- During 5 years (from 1998 to 2002), a total of ponent used as an overall index of size. The PCA 61 colonies of P. remot a were maintained at the scores were classified using the cluster member- Bee Laboratory (University of São Paulo) and in- ship, and the linear discriminant analysis was ap- spected regularly. To study queen size variation we plied to the PCA scores as described above. Both Queen size variation and egg laying 655 k-means procedure, the linear discriminant analy- queen, which emerged on the second day of record- sis, and the principal component analysis are rela- ing after the queen exchange in col. Pr3, we com- tively robust to the type of departures from normal- pared the first 24 h only. At this time the situation ity displayed by the studied variables (Tabachnick in both colonies was the same (i.e. no virgin queens and Fidell, 1989). were present). 2.2. EGG LAYING PERFORMANCE 2.2.3. Host colony experiment 2.2.1. Observation on daily oviposition Two colonies, Pr1 and Pr2, in similar conditions We performed another experiment with 5 other with respect to food storage and number of work- colonies. One of them, Pr5, was chosen as a host ers, but with a miniature and a normal-sized queen, colony to receive queens of different sizes from 4 respectively, were used for observations on ovipo- other colonies, Pr6 through Pr9, one at a time. In sition rate. The number of cells into which queens this way we guaranteed the environment was the oviposited was counted daily over a period of 19 same for all queens. The host colony was in very days (March, 13th to 31st, 1998) just before the good condition and was fed ad libitum with fresh typical interruption of cell construction (Benthem pollen of Tetragonisca angustula and Apis mellif- et al., 1995; Ribeiro et al., 2003b). A sheet of pa- era honey during the days of the experiment. This per with hexagonal figures was used to represent was done to stimulate a high cell construction rate. the comb. The cells which had been operculated ev- When the cells were almost ready, just before the ery 24 h were completed using coloured pencils. POP, the queen of the host colony was replaced by The total number of cells that were oviposited in an alien queen. This queen was allowed to oviposit per day by both queens was compared using a Chi- and the number of cells oviposited in was counted.