Sex in murky waters: algal-induced turbidity increases sexual selection in pipefish

Josefin Sundin,Anders Berglund,Gunilla Rosenqvist,Tonje Aronsen

doi:10.1007/s00265-017-2310-8

Abstract

Algal-induced turbidity has been shown to alter several important aspects of reproduction and sexual selection. However, while turbidity has been shown to negatively affect reproduction and sexually selected traits in some species, it may instead enhance reproductive success in others, implying that the impact of eutrophication is far more complex than originally believed. In this study, we aimed to provide more insight into these inconsistent findings. We used molecular tools to investigate the impact of algal turbidity on reproductive success and sexual selection on males in controlled laboratory experiments, allowing mate choice, mating competition, and mate encounter rates to affect reproduction. As study species, we used the broad-nosed pipefish, Syngnathus typhle, a species practicing male pregnancy and where we have previously shown that male mate choice is impaired by turbidity. Here, turbidity instead enhanced sexual selection on male size and mating success as well as reproductive success. Effects from mating competition and mate encounter rates may thus override effects from mate choice based on visual cues, producing an overall stronger sexual selection in turbid waters. Hence, seemingly inconsistent effects of turbidity on sexual selection may depend on which mechanisms of sexual selection that have been under study.Significance statementAlgal blooms are becoming increasingly more common due to eutrophication of freshwater and marine environments. The high density of algae lowers water transparency and reduces the possibility for fish and other aquatic animals to perform behaviors dependent on vision. We have previously shown that pipefish are unable to select the best partner in mate choice trials when water transparency was reduced. However, fish might use other senses than vision to compensate for the reduction in water transparency. In this study, we found that when fish were allowed to freely interact, thereby allowing competition between partners and direct contact between the fish, the best partner was indeed chosen. Hence, the negative effects of reduced water visibility due to algal blooms may be counteracted by the use of other senses in fish.

Highlights

Human-induced changes, such as climate change (Bradshaw and Holzapfel 2006), pollution (Carson 1962; Lurling and Scheffer 2007), selective harvesting (Law 2000; Coltman et al 2003), urbanization (Marzluff et al 2008), deforestation, and habitat fragmentation (Saunders et al 1991; Skole and 78 Page 2 of 8Behav Ecol Sociobiol (2017) 71: 78Tucker 1993), affect the abundance, distribution, and evolution of organisms
We have previously shown that sexual selection on mate size through mate choice of visual cues is impaired in turbid waters (Sundin et al 2010)
There was no relationship between male length and the mating probability in the clear treatment (GLMM: estimated slope ± SE = 0.003 ± 0.03, zvalue = 0.11, P = 0.91) (Fig. 1, Table 1)

Summary

Introduction

Human-induced changes, such as climate change (Bradshaw and Holzapfel 2006), pollution (Carson 1962; Lurling and Scheffer 2007), selective harvesting (Law 2000; Coltman et al 2003), urbanization (Marzluff et al 2008), deforestation, and habitat fragmentation (Saunders et al 1991; Skole and 78 Page 2 of 8Behav Ecol Sociobiol (2017) 71: 78Tucker 1993), affect the abundance, distribution, and evolution of organisms. Turbidity and increased algal cover may hamper species-specific sexual signaling, leading to hybridization in Lake Victoria cichlids (Seehausen et al 1997; Selz et al 2014) It can relax sexual selection on male nuptial coloration and courtship activity, diminishing honest signaling of mate quality and increasing the probability of reproduction for parasitized males, as shown in the three-spined stickleback (Candolin et al 2007; Wong et al 2007; Heuschele and Candolin 2010). Turbidity can further relax sexual selection on mate size and decrease parental care in the sand goby (Järvenpää and Lindström 2004, 2011), increase latency until courting in the desert goby (Michelangeli et al 2015), and decrease mate search and evaluation in the sailfin molly and in the three-spined stickleback (Heubel and Schlupp 2006; Heuschele et al 2012) All these studies show adverse effects of turbidity in traits and behaviors relevant for population viability. The object of this study is to increase our understanding on the effects of turbidity on sexual selection under more natural conditions by exploring additional mechanisms of sexual selection, such as mating competition and mate encounter rates

Objectives

Methods

Results

Discussion

Conclusion