The morphology and behavior of dimorphic males in Perdita portalis (Hymenoptera : Andrenidae)

Abstract

In Perdita portalis, a ground nesting, communal bee, males are clearly dimorphic. The two male morphs are easily distinguished based on head size and shape into (1) a flight-capable, small-headed (SH) morph that resembles the males of other closely related species and (2) a flightless, large-headed (LH) morph that possesses numerous derived traits, such as reduced compound eyes, enlarged facial foveae and fully atrophied indirect flight muscles. The SH morph occurs exclusively on flowers while the LH morph is found only in nests with females. While on flowers, SH males are aggressive, fighting with conspecific males and heterospecific male and female bees, and they mate frequently with foraging females. Using artificial observation nests placed in the field, I observed the behavior of females and LH males within their subterranean nests. LH males are aggressive fighters; males attacked each other with mandibles agape, and male-male fights always ended in the death of one male. LH males are highly attentive to the reproductive behavior of females; they spend increasing amounts of time near open cells during cell provisioning, and mating only takes place immediately prior to oviposition when females are forming the accumulated pollen and nectar into a ball. Based on larvae reared to adulthood in the laboratory, the two male morphs occur in equal proportions. The behavior of males in closely related species, especially P. texana, and the origin and maintenance of male dimorphism are discussed.

Emergence dynamics and bet hedging in a desert bee, Perdita portalis

“…The age structure of such nests is not clear and may include larvae of di¡erent ages (see below). Males in this species occur in two discrete, non-overlapping male morphs: large-headed, £ightless males (LH males) and small-headed, £ight-capable males (SH males) (Danforth 1991b). …”

Male mating behaviour and mating systems of bees: an overview

“…This is because receptive females of oligolectic species are more predictably aggregated at their host flowers whereas females of polylectic species are likely to be more widely distributed across flowering plant species. Note, however, that two of the species with a flower-based rendezvous site in Table II are oligolectic (Andrena agilissima and Macrotera (=Perdita) portalis) whilst two are polylectic (Anthidium manicatum and Osmia rufa) (Westrich, 1989;Danforth, 1991a;Seidelmann, 1999).…”

“…Though extended female receptivity decreases the temporal clumping of receptive females and therefore would tend to place a species lower down in Table I (receptive females are less predictable in time), it is unclear how it changes the degree to which males can monopolise mates against rival males. In M. portalis, for example, females mate immediately prior to laying an egg in an underground brood cell, therefore the communal nest is a highly predictable location of receptive females across the entire brood provisioning season (Danforth, 1991a).…”

“…For species with extended female receptivity (e.g. A. manicatum and M. portalis), large males are known to have high rates of copulation (Danforth, 1991a;Starks and Reeve, 1999). In ants, socalled 'ergatoid' males that mate repeatedly within the nest produce sperm into adulthood (Heinze and Hölldobler, 1993) whereas 'typical' males, that generally engage in scramble competition for mates, only produce one complement of sperm during larval and early adulthood that is not replenished following mating, limiting the number of partners with whom they can successfully mate (reviewed in Boomsma et al, 2005).…”

Evolution of dimorphic traits: effect of directional selection on heritability

“…The assumption underlying this analysis is that the continuous nature of the trait is phenotypically evident. But many traits occur as discrete, rather than continuously distributed, characters: for example, dimorphic variation in morphological structures in cladocera (Dodson,1 989), beetles and earwigs (Eberhard & Gutiérrez, 1991); thrips (Crespi, 1988), Hymenoptera (Danforth, 1991;Elmes, 1991); paedomorphosis in amphibia (Harris et a!., 1990); wing dimorphism in insects (Roff, 1986a); mating behaviour (see Table 7.7 in Roff, 1992); sex ratio (Bull et a!., 1982) and diapause . Although these traits appear phenotypically discrete, their inheritance may be polygenic, the particular manifestation of the trait being a function of a threshold of sensitivity.…”