Competition with filamentous fungi and its implication for a gregarious lifestyle in insects living on ephemeral resources

Abstract

1. Recent studies have demonstrated the existence of positive density dependence in the survival and development of Drosophila (the so-called Allee effect); however the underlying mechanisms of such Allee effects have remained elusive. Competition with filamentous fungi have often been suggested to be involved in causing high mortality at low larval density, but it has not yet been explicitly tested if the well known spatial aggregation of insect eggs yields a fitness benefit for the developing larvae in the presence of noxious moulds.2. Using Drosophila melanogaster, the present study tested whether larval survival is greater in aggregations when confronted with various combinations of three representative mould species (Aspergillus, Alternaria, and Penicillium) and a head start for fungal development.3. High rates of fungal-dependent mortality and significant positive densitydependent larval survival (i.e. Allee effects) were observed when larvae were confronted with food resources containing established colonies of Aspergillus or Alternaria. Neither the simultaneous transfer of Aspergillus or Alternaria spores with larvae to food patches nor food infections with Penicillium affected insect larval development.4. Significant correlations between mould growth and larval survival could be identified, although the patterns that emerged were shown to be inconsistent when the effects were compared between fungal species and fungal priority. Because mould growth only partly explained larval survival, the influence of other fungal-borne factors, e.g. mycotoxins, needs to be elucidated in order to understand the mechanistic basis of insect-mould interactions.5. These results are the first to argue convincingly for moulds being involved in mediating Allee effects for insects on ephemeral resources; however they also demonstrate an unexpected diversity in insect-mould interactions. Considering this diversity may be important in understanding insect spatial ecology.

Visual attraction in Drosophila larvae develops during a critical period and is modulated by crowding conditions

“…While Drosophila larvae can show social behavior, they also survive well in isolation in the lab. However, survival in isolation may not be the case in a field setting (Rohlfs et al 2005;Venu et al 2014). It is intriguing that larvae can combine visual recognition with an assessment of food conditions.…”

Social attraction mediated by fruit flies' microbiome

“…While adult and larval fruit flies can taste a substrate in order to obtain some information about food quality, taste alone cannot indicate the presence of all essential nutrients. Furthermore, fruit flies are under intense competition with numerous species of fungi and bacteria for feeding on fallen fruit, and many microbes produce secondary compounds that harm other microbes as well as many other animals, including fruit flies (Janzen, 1977;Demain and Fang, 2000;Rohlfs et al, 2005;Rozen et al, 2008). It is thus possible that microbiome volatiles signal to flies the availability of a food substrate with suitable microbial species.…”

“…Another possible benefit of gut bacteria is suppression of competing or harmful microbial species. Mould can cause high rates of mortality among fruit fly larvae, and groups of larvae can suppress mould growth as well as enhance the growth of certain yeast species (Rohlfs et al, 2005;Stamps et al, 2012). Intriguingly, both species of Lactobacillus we have studied produce compounds that suppress fungal and bacterial growth (Ruiz-Barba et al, 1994;Laitila et al, 2002;Schnürer and Magnusson, 2005;Mauch et al, 2010;Crowley et al, 2012).…”

Antimicrobial strategies in burying beetles breeding on carrion

“…Despite the ubiquity of animal-microbe competition in nature, experimental tests of Janzen's hypotheses are limited, in particular with respect to antimicrobial strategies in animals other than avoidance (5,6) that would allow animals to use microbe-laden resources (7). Furthermore, there is little information on the adaptive consequences to animals of microbial competition (8). Such data are now needed to advance our understanding of the evolutionary and ecological implications of competition between animals and microbes.…”