Mate selection based on labile traits affects short-term fitness in a long-lived seabird

Abstract

In long-lived monogamous social species, partner compatibility can play a crucial role in reproductive success. We evaluated assortative mating based on body condition (plasma triglyceride concentration), diet (δ¹⁵N), and foraging habitat (δ¹³C) in the blue-footed booby Sula nebouxii, a long-lived monogamous seabird. We investigated the effects of assortative mating (sum of triglycerides in a pair) and asymmetry within pairs (residuals from regression of female-male triglycerides) on reproductive performance and offspring growth (alkaline phosphatase, ALP). We found that strong assortative mating determined by body condition and diet seemed to be related to a signalling mechanism (nutritional state). This mating pattern had a substantial effect on the breeding parameters and influenced offspring ALP. Within-pair asymmetry did not influence any reproductive parameters, but the ALP of offspring was related to the within-pair relative female condition. Overall, our results indicate that individuals seek the best possible match to maximize their breeding investment and/or individuals are limited in their mate options by their current body condition, which has consequences for offspring fitness in the short term. Our findings show that assortative mating based on body condition produces notable variation in the joint condition of the pair, which determines their breeding success.

Keywords: alkaline phosphatase; assortative mating; labile traits; stable isotopes; triglyceride.

Figure 1.

Correlation of triglyceride concentration between members of pairs of blue-footed boobies (Sula nebouxii) sampled from the Isla El Rancho colony in Sinaloa, Mexico, during the courtship period.

Figure 2.

Correlations of blood δ¹⁵N and δ¹³C values between members of pairs of blue-footed boobies (Sula nebouxii) sampled from the Isla El Rancho colony in Sinaloa, Mexico, during the courtship period.

Figure 3.

Relationship between the sum of triglyceride concentrations per pair of blue-footed boobies (Sula nebouxii) during the courtship period and total egg volume (sum of individual egg volumes in the clutch).

Figure 4.

Relationship between the sum of triglyceride concentrations per pair of blue-footed boobies (Sula nebouxii) during the courtship period and (a) hatching success (data and estimated probability) and (b) fledging success (data and estimated probability depending on hierarchy). Fitted lines are derived from generalized linear models.

Figure 5.

Relationship between the alkaline phosphatase concentration of the first chicks and (a) the sum of triglyceride concentrations per pair of blue-footed boobies (Sula nebouxii) and (b) the asymmetry within each pair (measured as the residuals from a regression of female and male triglyceride concentrations). A value less than 0 indicates that the female had a lower triglyceride concentration than expected based on the male triglyceride concentration, and a value greater than 0 indicates that the female had a higher triglyceride concentration than expected.