Pegoscapus is a genus of fig wasp native to the Americas. They range from Florida and Mexico in the north to Argentina in the south. Fig wasps have an obligate mutualism with the fig species they pollinate. Pegoscapus pollinates species in section Americana of the subgenus Urostigma.
The genus is estimated to be 28 million years old using cytochrome oxidase nucleotide sequences, and more than 20 million years old based on a fossil in amber from the Dominican Republic.
Habitat Pegoscapus is a genus of fig wasp in the family Agaonidae. As a pollinating fig wasp, Pegoscapus share an obligate mutualistic relationship with fig trees of the genus Ficus via association with fig inflorescences (syconia), commonly called figs. Males are smaller in size with shorter antennae than females. Males have a black head and amber-colored, wingless body. Females, however, have wings. Pegoscapus are native to the Americas, ranging from Florida to Mexico.Moisset B. Fig Wasps. U.S. Forest Service.
Mutualism Fig wasps belonging to the genus Pegoscapus share an obligate mutualistic relationship with fig trees of the genus Ficus via association with fig inflorescences. The fig wasp and fig tree aid one another in their reproductive cycles. In their larval and reproductive stages, Pegoscapus wasps are confined to figs which provide protection and nutrients. Adult females exit the fig, collecting pollen, which they deliver to another fig inflorescence, therefore aiding in the fig reproductive cycle. This pollination mutualism has led to fig wasps developing honed morphological adaptions such as thoracic pockets to carry pollen with their forelegs to later deposit on the stigmatic surface of another fig during oviposition. Additionally, it has caused Pegoscapus to develop extreme host specificity and life cycles synchronized with the fig's reproductive cycle. For example, oviposition by fig wasps coincides with the receptivity of fig flowers, and the release of adult wasps aligns with pollen presentation. Fig phenology allows asynchronous fig development resulting in receptive figs year-round for Pegoscapus wasps.Weiblen G.D. How to be a Fig Wasp. (2002). Annu. Rev. Entomol. 47, 299-330. doi: https://doi.org/10.1146/annurev.ento.47.091201.145213
Pegoscapus wasps lay eggs in fig trees' ovules. Each wasp larva feeds on a singular fig tree ovule. An ovule can therefore become a seed if pollinated or a "wasp gall" when the egg is deposited in it. The ovule cannot become both a seed and wasp gall. However, Pegoscapus do not oviposit in all fig ovaries even when the fig has enough female wasps with enough eggs to do so. The mutualism between figs and Pegoscapus persists in part due to the failure of all wasps to translate all of their eggs to offspring as. If they did translate all their eggs, the fig tree would not be able to produce seeds and reproduce. This occurs because some eggs and larvae are inviable or are victims of plant defenses. Moreover, lifetime reproductive success of female wasps entering the syconium is unaffected by a lack of oviposition in all fig ovaries, so this adaptation to maintain the mutualism is not harmful to Pegoscapus. Female wasps that enter a syconium are known as foundresses.
Reproduction and development The life and pollination cycles of Pegoscapus species varies because of the variability in fig species' inflorescence morphology that comes with being a monoecious or dioecious fig. This fig tree variability correlates with variability in fig wasp morphology in terms of pollen collection and oviposition mechanisms in order to maintain the fig wasps' and fig trees' reproductive cycles. These differences between Pegoscapus species are good characteristics for phylogenetic inferences. However, the life and pollination cycles detailed here of monoecious Ficus aurea and Ficus citrifolia and their respective pollinators, Pegoscapus asseutus and Pegoscapus jimenezi, are representative of the general trends in Pegoscapus reproductive cycles.Frank S.A. The Behavior and Morphology of the Fig Wasps Pegoscapus Assuetus and P. Jimenezi: Descriptions and Suggested Behavioral Characters for Phylogenetic Studies. (1984). Cambridge Entomological. 91, 289-308.
Monoecious syconia of these species have a globular inflorescence with pistillate and staminate florets lining a sealed cavity. The entrance into the cavity is blocked by scales during early development of the syncoium. To assess the developmental stage of the syconia and therefore its readiness for her to enter, female Pegoscapus touch the entrance with her antennae to determine the looseness of the blocking mechanisms of the fig. If loose, she passes through the tight entrance, and her wings and some antennae detach. Some fig wasps cannot fully enter and die within the entrance.
Foundresses enter the central cavity of the syconium. The eggs are oviposited into the ovary of pistillate floret resulting in wasp galls. The larvae develop there while feeding on developing seed tissues or the seed itself. After each oviposition, pollen is spread nearby via various behavioral mechanisms. Usually two or more foundresses oviposition and pollinate one syconium simultaneously. After oviposition, the foundresses die in the central cavity while the larvae and seeds continue to develop.
After 27-32 days, the central cavity swells, and males exit the ovaries where they developed. Males make up the minority of the offspring generation, lack wings, and have reduced eyes. They search for mature females that remain in the floral ovaries where they developed. The males chew holes in the ovaries and insert their abdomens to mate with the females. Multiple males begin chewing an exit tunnel in the syconium wall, and then all males die. Females widen the exit hole and emerge into the central cavity. They begin searching for anthers still containing pollen, ensuring a large enough amount of pollen is collected before exiting the tunnel. The foundresses find another receptive syconia, pollinate it, and begin the cycle once more.
Male morphology A common characteristic of male Pegoscapus is the seminal vesicle which produces fluids used to complete ejaculation. The seminal vesicle has two morphologically distinct anterior and posterior portions. The anterior portion stores mature spermatozoa and aides in reabsorption and digestion of defective cells and sperm fluid. The anterior portion is reported to occur in other fig wasp genera as well. Unlike other fig wasp genera, Pegoscapus has a second posterior seminal vesicle portion for ejaculation that is suggested to ensure only a small amount of stored spermatozoa are ejaculated per sexual copulation. This is important as it provides each short-lived male with the ability to mate with many females rapidly and in succession. Spermatozoa length and thickness differs between Pegoscapus species.Fiorillo B.S., Lino-Neto J., Báo S.N. Structural and ultrastructural characterization of male reproductive tracts and spermatozoa in fig wasps of the genus Pegoscapus (Hymenoptera, Chalcidoidea) (2008). Micron. 39(8), 1271-1280. doi:10.1016/j.micron.2008.03.005
Female lethal combat Female Pegoscapus show no aggression within or outside of the fig prior to any foundress ovipositing. However, the first foundress to oviposit in a non-specified Pegoscapus species has been found to become aggressive. This led to lethal combat and the death of the competitor by the first foundress. Injury, especially decapitation, was found to be effective at reducing competitors’ oviposition rates. In comparison to the non-specified Pegoscapus species, little aggression has been found in Pegoscapus tonduzi in similar contests. However, there were on average fewer foundresses per syconium in Pegoscapus tonduzi'''s native region of Panama. This suggests reduced aggression in this species is due to less competition for syconia as oviposition sites which are essential to successful reproduction.Dunn D.W., Jandér K.C., Lamas A.G., Pereira R.A.S. Mortal combat and competition for oviposition sites in female pollinating fig wasps. (2014). Behavioral Ecology. 26(1), 262-268. DOI:10.1093/beheco/aru191
Speciation The global and local diversity of Ficus and Pegoscapus species has been difficult to explain based on the assumption of strict sense cospeciation and one-to-one pollinator specificity. Therefore, there is no generally accredited mechanisms on the speciation of figs and their pollinators. However, it has been suggested that hybridization and introgression due to pollinators switching and sharing hosts are the major mechanisms causing diversity of fig and wasp species.Machado C.A., Robbins N., Gilbert M.T.P., Herre E.A. Critical review of host specificity and this coevolutionary implications in the fig/fig-wasp mutualism. (2005). Proc. Of the National Acad. Of Sci. of the U.S.A.102(1), 6558-6565. doi: 10.1073/pnas.0501840102
Hybridization between Pegoscapus species results in new genotype combinations causing diversification and evolution of specialized pollinators. Inbreeding that occurs in Pegoscapus reinforces this divergence by causing these new genotype combinations to persist in the population. Coevolution of mutualism occurs because groups of genetically well defined wasp species tend to coevolve with genetically less well defined (frequently hybridizing) groups of figs. Since the fig trees have more variance in genotype, the wasp species must continually acquire adaptations to maintain the obligate mutualism in order to survive. Inbreeding reinforces these adaptations.
Cryptic species Many fig trees may commonly be pollinated by several cryptic species. Microsatellite loci are vital when distinguishing cryptic Pegoscapus species for evolutionary and population genetic studies.Molbo D., Krieger M.J.B., Herre E.A., Keller L. Species-diagnostic micro satellite loci for the fig wasp genus Pegoscapus. (2002). Molecular Ecology Notes. 2(4), 440-442.
https://doi.org/10.1046/j.1471-8286.2002.00268.x Coexistence of cryptic fig wasp species within a single host fig species has been proven by genetic data via mitochondrial sequence differences implying old divergences. Some of the cryptic species’ pairs appear to be sister taxa, providing evidence for the long-term coexistence of shared hosts/colonization of novel fig species. These findings contest the strict one-to specificity between cospeciating figs and pollinators.Molbo D., Machado C.A., Sevenster J.G., Keller L., Herre E.A. Cryptic species of fig-pollinating wasps: Implications for the evolution of the fig-wasp mutualism, sex allocation, and precision of adaptation. (2003). PNAS. 100(10), 5867-5872. https://doi.org/10.1073/pnas.0930903100
Local mate competition, inbreeding, and sex ratios
Local mate competition (LMC) occurs when mating takes place among offspring of one or a few mothers in a discrete population. This causes brothers to compete with one another for mating partners. LMC increases inbreeding levels due to brothers competing for their own sisters as mates; this therefore increases mother-offspring relatedness. LMC favors female biased sex ratios because more females and fewer males reduces competition between males and increases mating opportunities for males. LMC occurrence is therefore supported by instances of isolated populations, high levels of inbreeding, and female biased sex ratios.Pereira R.A.S., Prado A.P. Effect of Local Mate Competition on Fig Wasp Sex Ratios. (2006). Braz. J . Biol. 66(2B), 603-610. https://doi.org/10.1590/S1519-69842006000400004