Social organization, reproductive behavior and ecology of Leptothorax acervorum (Hymenoptera, Formicidae) from the Sierra de Albarracin in central Spain

Abstract

Leptothorax acervorum, an ant species with holarctic range, occurs in an isolated population in the Spanish Sierra de Albarracin. Dissection of dealate females and laboratory observations revealed that in contrast to other European populations, the colonies are monogynous, with one reproductive queen each and a variable number of virgin or mated dealate but not laying females. Most of the latter probably just hibernate in the mother nests, leaving them in the following spring, but a few remain there for longer time, without reproducing. Such colonies then are functionally monogynous. Alate females exhibit a stationary sexual calling, and mating behavior could be studied in the laboratory. Mated females return to the mother nest where they soon shed wings. When developing fertility before or after hibernation they are evicted from the nests; in nature they probably form daughter colonies. Patchy habitat and rough climatic conditions in the Sierra de Albarracin may be responsible for the particular reproductive behavior of L. acervorum in this area. The generally small size difference between queens and workers in the subgenus Leptothorax entails high costs of dispersal and colony foundation by single queens who have to forage for their first brood. Some kind of dependent colony foundation therefore is frequently met with in the subgenus. Notwithstanding the marked biological and a few slight morphological differences between central European L. acervorum and the Spanish population its taxonomic status as yet is unsettled. We refer to this population provisionally as "L. acervorum Albarracin".

Polymorphic social organization in an ant

“…Furthermore, the type A queen was, in most cases, genetically compatible with being the mother of the majority fullsibling family (exceptions discussed below), and no type C or D queen was compatible with being the mother of any other colony member. These data confirm a previous report of functional monogyny (Felke & Buschinger 1999).…”

“…Functional monogyny has also been reported in multiple queen colonies of the ant Leptothorax acervorum (Ito 1990;Seppa et al 1995;Felke & Buschinger 1999). This is intriguing as studies of UK and central European populations show multiple queen colonies to be polygynous (low skew) based on strong and comprehensive evidence, including data on egg maternity (Hammond et al 2006), low nestmate relatedness (Douwes et al 1987;Stille et al 1991;Chan & Bourke 1994;Heinze et al 1995a,b;Bourke et al 1997;Hammond et al 2001), queen ovary development, and behaviour (Buschinger 1968;Bourke 1991Bourke , 1993Heinze et al 1995b).…”

“…By contrast, the evidence for functional monogyny is weaker. Ovary dissections and observations of colonies suggest that a single queen is reproductive in multiple queen colonies from a population in Spain (Felke & Buschinger 1999) and that reproduction is heavily biased towards one queen in multiple queen colonies from Japan (Ito 1990). In addition, two genetic studies using allozyme data revealed high relatedness among workers in populations from Finland (Seppa et al 1995) and Spain (Heinze et al 1995a), but crucially queen number and mating status in the studied colonies was unknown.…”

“…In addition, two genetic studies using allozyme data revealed high relatedness among workers in populations from Finland (Seppa et al 1995) and Spain (Heinze et al 1995a), but crucially queen number and mating status in the studied colonies was unknown. It has been suggested that the presence of non-reproductive queens may be because newly mated queens are simply overwintering before dispersing, rather than a stable social organization, and that functionally monogynous populations may be a different species (Felke & Buschinger 1999).…”

A test of reproductive skew models in a field population of a multiple-queen ant

“…In addition, the presence of subordinates increases the productivity of dominant queens, although the mechanism underlying this effect is unclear (Heinze and Oberstadt 2003). Consistent with concession models, broad-scale comparisons in leptothoracines (i.e., at the between-population and between-species level) suggest positive correlations of skew with relatedness (Heinze 1995;Heinze et al 1995b;Bourke et al 1997) and inferred levels of ecological constraint (Bourke and Heinze 1994;Felke and Buschinger 1999). In contrast, a comprehensive study of L. rugatulus on skew variation among colonies (which either had been kept in the laboratory for 11 months or were artificially composed) found no support for concession models (Rüppell et al 2002).…”