Colony size and brood investment of Myrmica rubra ant colonies in habitats invaded by goldenrods

Abstract

Ant richness and abundance are negatively affected by the invasion of alien goldenrods (Solidago sp.). However, little is known about the mechanisms standing behind the impact of the invaders on ant life history, such as colony investments in growth and reproduction. We examined this problem of the investments of Myrmica rubra ant colonies living in different grasslands invaded and non-invaded by goldenrods. Altogether, 47 colonies were analysed; and for each colony, we calculated the number of queens, workers and the production of young workers, gynes, and males. We found that colonies from invaded meadows are smaller in size, but have a similar number of adult queens compared to colonies from non-invaded sites. We also found different brood investments among colonies from invaded and non-invaded meadows—colonies from non-invaded meadows produce more young workers and invest more in growth, whereas colonies from invaded meadows invest more in reproduction through higher gyne production. Male production was at a similar level in colonies from both habitat types. The observed patterns may be explained by the effect of various environmental factors occurring in both grassland types, such as stress in changed habitats, higher competition among gynes in non-invaded grasslands, or finally, by the adaptive colony-level response of ants to stress. The higher production of gynes observed in the invaded grasslands may support dispersal and enhance the probability of establishing a colony in a more favourable location.

Habitat features and colony characteristics influencing ant personality and its fitness consequences

“…Invasive plants can induce negative changes in ground-dwelling arthropod assemblages ( Schirmel et al 2011 ; Gallé et al 2015 ), usually by altering habitat structure ( Hejda et al 2009 ), but also by changing the nesting site ( Somogyi et al 2017 ) or food availability ( Lenda et al 2013 ; Trigos-Peral et al 2018 ). The results of our previous studies performed on M. rubra ants living in meadows invaded by Solidago plants ( Lenda et al 2013 ; Grześ et al 2018 ; Trigos-Peral et al 2018 ) suggest that there can be different selective pressures on ant colonies living in these two habitat types thus we expected to find the differences in individual and/or colony personalities. Our results did not demonstrate such differences but found that the behavior of Myrmica workers and colonies can differ at three levels of variation (among- and intraindividual variation, and also in residual variation).…”

“…Higher Myrmica nest density results in lower predictability of individual activity but allospecific nest density had an opposite effect (foragers had higher predictability in their activity). This can highlight the importance of competition for food and nesting sites which has an enhanced effect on seminatural meadows (see also Lenda et al 2013 ; Grześ et al 2018 ). Competition is usually considered to have a significant effect in shaping ant communities ( Savolainen and Vepsäläinen 1988 ; Braschler and Baur 2003 ; Trigos-Peral et al 2016 ), and unavoidably occurs when the ecological requirements of species overlap ( Pianka 1974 ; Glen and Dickman 2008 ).…”

“…On the individual-level, different habitat types can change the effect of different behavioral traits on productivity. It seems that in seminatural meadows ( Lenda et al 2013 ; Grześ et al 2018 ; Trigos-Peral et al 2018 ), where higher nest densities occur, selection acts mostly for the aggression of workers that can result in increased overall productivity (see also Modlmeier and Foitzik 2011 ). The higher nest density can also lead to frequent encounters with foragers of other colonies ( Hölldobler and Wilson 1990 ), so a more targeted path (lower meandering) when gathering resources can also enhance productivity.…”

“…The same model construction but separate models were used for testing the effect of different behavioral traits on the number of new gynes (gyne pupae + winged), males (male pupae + winged), and workers (larvae + worker pupae). Having information already about the effect of different habitat type (invaded vs. seminatural) on colony productivity parameters ( Grześ et al 2018 ), the analyses on the effect of the different individual behavioral traits were conducted separately for the two habitats types ( N seminatural = 366, N invaded = 315). New males were found only in a low number of colonies from the invaded habitats, so the results of these analyses were not included.…”

“…plants. Our previous studies performed on ants inhabiting these two habitat types demonstrated different brood investments ( Grześ et al 2018 ) and that Myrmica ant colonies living in invaded meadows are smaller in size and also have lower nest densities ( Lenda et al 2013 ; Grześ et al 2018 ; Trigos-Peral et al 2018 ). Moreover, workers have to forage over longer distances probably because protein resources are the main limiting factor in invaded meadows ( Lenda et al 2013 ; Trigos-Peral et al 2018 ).…”