Egg-mediated maternal effects in a cooperatively breeding cichlid fish

Abstract

Mothers can influence offspring phenotype through egg-mediated maternal effects, which can be influenced by cues mothers obtain from their environment during offspring production. Developing embryos use these components but have mechanisms to alter maternal signals. Here we aimed to understand the role of mothers and embryos in how maternal effects might shape offspring social phenotype. In the cooperatively breeding fish Neolamprologus pulcher different social phenotypes develop in large and small social groups differing in predation risk and social complexity. We manipulated the maternal social environment of N. pulcher females during egg laying by allocating them either to a small or a large social group. We compared egg mass and clutch size and the concentration of corticosteroid metabolites between social environments, and between fertilized and unfertilized eggs to investigate how embryos deal with maternal signalling. Mothers in small groups produced larger clutches but neither laid smaller eggs nor bestowed eggs differently with corticosteroids. Fertilized eggs scored lower on a principal component representing three corticosteroid metabolites, namely 11-deoxycortisol, cortisone, and 11-deoxycorticosterone. We did not detect egg-mediated maternal effects induced by the maternal social environment. We discuss that divergent social phenotypes induced by different group sizes may be triggered by own offspring experience.

Figure 1

Egg mass of individual females under the two different group size conditions. The clutches of spawning 1 are represented by orange circles and the ones from spawning 2 by purple triangles.

Figure 2

(a) Clutch sizes in the different group size treatments. The clutches of spawning 1 are represented by orange circles and the ones from spawning 2 by purple triangles. (b) Clutch size as a function of mother body condition. The body condition was calculated using Fulton’s index.

Figure 3

PCA of the four corticosteroid metabolites identified the fish eggs for samples of both group sizes and fertilization states. (a) Large (blue circles) and small (red triangles) groups. (b) Fertilized (orange circles) and unfertilized (purple triangles) eggs. In both panels, individual samples are depicted with small symbols whereas the mean value of each group size is depicted with large symbols.

Figure 4

Schematic representation of the egg collection sequence. A breeder pair was assigned either to a small or to a large social group. In each group, breeders produced up to four clutches (i.e., 1,2,3, and 4). The first clutch (light blue box) was removed and discarded. The 2nd and 4th clutches were allowed to hatch and young to grow up in the social groups (dark blue boxes). The 3rd clutch (spawning 1, i.e., orange circle) was either unfertilized or freshly fertilized and collected for analysis for this study. After the 4th clutch, the breeding pair was assigned to a new set of helpers either in a small (dotted arrow) or large (solid arrow) and the eggs of spawning 2 (i.e., purple triangle; unfertilized or freshly fertilized) were collected following same procedure described for spawning 1.