Merizodus soledadinus density

Daly, Ella & Renault, David, 2025, Experimental tests of feeding behaviour, dietary breadth and cooperative feeding in a predatory carabid invading sub-Antarctic regions, Antarctic Science (Cambridge, England) 37 (3), pp. 167-175 : 169

Merizodus soledadinus density experiment

In a first part of the study, we investigated the importance of density on the predatory behaviour of M. soledadinus , as lone individuals may not be capable of taking on all prey species effectively. To do this, we presented different prey types to single M. soledadinus individuals and groups of 10 individuals (see Table I for number of trials per species). The prey used were larval dipteran Calycopteryx moseleyi Eaton, 1875 , annelid M. kerguelarum Grube, 1877 and larval lepidopteran P. kerguelensis Enderlein, 1905 . As with the prey choice experiment, predators fasted for 1 week prior to the start of the experiment. The fasting period and experiments were conducted at 8 ○ C by holding adult M. soledadinus individually in Petri dishes covered with filter paper on their bases and moistened with tap water.

The experiments were conducted in Petri dishes (diameter: 9 cm). For trials with a single M. soledadinus individual, the invertebrates were initially observed for a period of 1 h, with behavioural observations taken after 1, 30 and 60 min. The time of first contact, defined as the time at which the antennae or mandibles of one adult M. soledadinus first touched the prey, was also noted when it occurred within this first hour. Each Petri dish was then left for a period of 24 h, at which point a final observation of the remaining prey was taken. For trials with 10 M. soledadinus individuals, the invertebrates were observed for 1 h or until nothing remained of the prey, if that occurred before the hour had elapsed. We recorded the times of first contact between one, two, three and four or more M. soledadinus individuals and the prey.

To determine whether prey type or predator abundance influenced the initiation of predatory behaviour, we compared the time to first contact with prey across prey type and predator abundance as well as prey mortality after 5 h. For the time to first contact, we used a Kruskal-Wallis test as the data were not normally distributed (W = 0.754, P <0.05). We were interested in determining whether the presence of other adult individuals reduced the decision time to attack, as has been shown in other species ( Gamberale-Stille 2000). Similarly, we were interested in how decision time differed for M. soledadinus depending on prey type. We determined this using a Dunn’s test to examine pairwise differences. To compare prey mortality across groups, we tested for significant differences using a two-sided Fisher’s exact test.

Prey choice experiment

Adult M. soledadinus individuals were offered different potential prey species to assess their dietary breadth. The prey species used were a mix of native and introduced invertebrates from the orders Coleoptera , Diptera , Lepidoptera and Haplotaxida (Table II). These species were chosen because they are abundant and widely distributed within the Kerguelen Archipelago, and they represent the major non-predatory macroinvertebrate groups present in the same habitats as M. soledadinus (i.e. fellfield, tundra and coastal). The offered prey also included juvenile M. soledadinus because predation of larvae by adults has been observed in the field. All individuals used in these experiments - prey and M. soledadinus - were manually collected along the coast from the research stations Port-aux-Français (70 ○ 12’59.76”E, 49 ○ 21’0.00”S) and Baie de l’Aurore Australe (70 ○ 11’10.50”E, 49 ○ 20’56.51”S).

Trials were carried out in Petri dishes (diameter: 9 cm). The bottoms of the Petri dishes were covered with filter paper so that the insects were able to move more easily and to provide humid conditions through wetting of the paper with tap water. Predators fasted for 1 week prior to the start of the experiment. Prey individuals, alone or in combination with another of the same or different prey species, were placed in the Petri dishes prior to the introduction of the predators. We varied the number of M. soledadinus individuals to obtain different prey:predator ratios (1:1, 1:2, 1:5, 1:10 and 1:20) because this predator species is frequently found in high densities, especially under stones in fellfield areas at the Kerguelen Archipelago. In the Kerguelen Archipelago, the average monthly temperature ranges between 2 ○ C in the winter and 8 ○ C in the summer months ( Frenot et al. 2001), although temperatures have been increasing recently ( Daly et al. 2023a). We conducted this experiment under two different temperature conditions typical of the daytime in the sub-Antarctic Kerguelen Archipelago during winter and summer periods (4 ○ C and 10 ○ C) and one appreciably above such temperatures (15 ○ C) to capture a range of temperatures, allowing for the estimation of potential changes in invertebrate predator behaviour as a function of environmental conditions (Table II). Due to constraints on the availability of prey individuals and limits on collecting wild individuals from the local natural reserve, not all conditions could be tested for all species. For summaries of conditions by species and number of replicates by combination, see Tables II & III, respectively.

M. soledadinus individuals were presented with either one or two prey individuals and were left with the prey for 24 h, after which we recorded the status of the prey as intact, partially consumed or totally consumed. Prey partially eaten but still alive within the observation period were considered partially consumed. We binary transformed our outcome (intact, partially consumed or totally consumed), with prey described as either consumed or intact. We used binary logistic regression to model predation by M. soledadinus during the first hour of the trial and at the end of 24 h with prey taxonomy, temperature (4 ○ C, 10 ○ C or 15 ○ C), prey type (species), origin (i.e. native or non-native species), life stage (juveniles (larvae, nymph), pupae or adult) and predator density for the consumption of prey. Also included in the model was whether or not alternative prey were offered. We fitted several models using the ‘drop1’ function in the base R package stats (R Core Team 2023) and compared these to a simple model based on the life history traits of M. soledadinus in order to better understand what influences predatory behaviour in this species.