Acromyrmex ameliae

Acromyrmex ameliae is a species of New World ants of the subfamily Myrmicinae. This species is from one of the two genera of advanced fungus-growing ants within the tribe Attini. It is found in the wild naturally in South America in Minas Gerais, Brasil.

Overview

Commonly known as "leaf-cutter ants", they are a species from one of the two genera within the tribe Attini. Acromyrmex can be identified from the closely related Atta genus of leafcutter ants since they have four pairs of spines and a rough exoskeleton on the upper surface of their thorax.

Like Atta, Acromyrmex subsists mostly on a particular species of fungus (genus Leucocoprinus), which it cultivates on a medium of masticated leaf tissue. This is the sole food of the queen and other colony members that remain in the nest. The media workers also gain subsistence from plant sap they ingest whilst physically cutting out sections of leaf from a variety of plants.

Acromyrmex species exhibit a high degree of biological polymorphism, four castes being present in established colonies - minims (or "garden ants"), minors, mediae, and majors. Majors are also known as soldiers or dinergates. Each caste has a specific function within the colony. Acromyrmex ants are less polymorphic than the other genera of leafcutter ants Atta, meaning comparatively less differential in size exists from the smallest to largest castes of Acromymex. The high degree of polymorphism in this genus is also suggestive of its high degree of advancement.

A. ameliae is a social parasite with much smaller reproductives (females and males) than those of its hosts A. subterraneus subterraneus and A. s. brunneus . Morphometrically, the A. ameliae queen is not a simple miniature of its hosts' queens, like Myrmica microrubra and its host Myrmica rubra. The species can be distinguish from the host using its propodeal spines: they are straight and laterally compressed unlike A. subterraneus subspecies, where they are slight to strongly curved and conical. A. ameliae differs from Acromyrmex insinuator (another social parasite) not only by its size and color (brown dark against yellowish-orange), but also it does not present a single strong median ruga extending from the central ocellus to the level of the posterior borders of lateral ocelli, like A. insinuator. On the contrary, around its central ocellus, the cuticle is wholly rugous without a distinct median ruga. In A. insinuator, the anteroventral edge of the postpetiole is broadly and evenly concave, without a broad median anteroventral extension. The anteroventral portion of the postpetiole in A. ameliae has irregular extensions, without the concavity present in the first species.

As in A. insinuator, reproductives of A. ameliae very much resemble the host species, although with a pronounced reduction in body size. From observations of nuptial flights that occurred in the laboratory, a mating flight is suspected to occur in the wild, but are yet to observed. Alate parasites are found in two different seasons (April and October), unlike the host species, which has only a single synchronized nuptial flight per year in November and December. More than one nuptial flight each year could increase the likelihood of successful invasion of new colonies by A. ameliae. The well-defined nuptial flight of the hosts is normally observed in November and December so that newly fertilized parasite A. ameliae queens (produced in April) can colonize established colonies of A. s. subterraneus and A. s. brunneus well before they reproduce themselves.

Like A. insinuator, A. ameliae is one of the rare inquiline parasites that produces workers and resembles its host in morphology, but unlike A. insinuator, A. ameliae queens differ dramatically from their host queen in size. In all colonies of A. subterraneus sampled in A. ameliae range, all of them were parasitized by A. ameliae. Thus, A. ameliae appears to be very common, yet until recently has been overlooked, suggesting the possibility that many other species of social parasites exist that have yet to be identified.

As in A. insinuator, A. ameliae produces a workforce that is essential for the production of the parasite alates, but this trait is being selected against over evolutionary time, although it has not yet been lost.

See also

• List of leafcutter ants

References