MICROSÍLICE.

Guppies have been a popular feature in aquariums and laboratories throughout much of the 20th_{and 21}st_{centuries. Consequently, accidental escapes and} orchestrated releases (largely in attempts to control mosquitos) have led to the guppy becoming established in at least 72 countries outside of its native range (Deacon et al. 2011). In a number of these countries it has been observed that guppies have a negative impact on local fish assemblages by out-competing them for space and resources while their efficacy as a mosquito control agent varies is unclear (Deacon 2010).

A feature of guppies both in Trinidad and abroad is their ability to adapt to novel and sub-optimal environments. In lab experiments guppies have been shown to tolerate a broad range of environmental conditions including temperature (Gibson and Hirst 1955, Chung 2001) and salinity (Gibson and Hirst 1955, Chervinski 1984) andin situstudies have shown the guppy to be tolerant of and abundant in degraded habitats and poor environmental conditions (Winemiller et al. 1990, Casatti et al. 2006). Many studies have been shown guppies to be

phenotypically plastic (e.g. Reznick and Bryga 1987, Reznick 1990, Kelley et al. 2003, Magellan et al. 2005). This flexibility, in combination with an omnivorous feeding strategy (Dussault and Kramer 1981), capacity for rapid life history

evolution (Reznick et al. 1990), plus the ability of a single female to establish a sustainable population (Carvalho et al. 1996, Deacon 2010) means that guppies have many of the characteristics identified as important for enabling successful invasion (Garcia-Berthou 2007).

Recent studies using transplant and mesocosm experiments have demonstrated that the local adaptions by guppies have the capacity to cause

ecosystem-level effects and be a potential driver of evolutionary change (Palkovacs et al. 2009, Bassar et al. 2010). Consequently the effect of a successful colonisation has eco-evolutionary consequences for the guppies, the invaded ecosystem and the organisms and processes therein (Palkovacs et al. 2009).

For freshwater fish, introduction into new environments often requires anthropogenic assistance (Reznick and Ghalambor 2001). Once present in the novel environment, the abiotic conditions faced are considered key to the success or failure of an invasion (Moyle and Light 1996a, b). The ability of guppies to persist despite widely differing thermal regimes that exceed the range of temperatures encountered in Trinidad appears a critical step to their successful establishment (for example at a site where guppies are present in central Mexico, over a two week period water temperatures varied between 17⁰C and 21⁰C,

Appendix 1).

The guppy’s ability as an invasive species is well documented and temperature is one of the main factors restricting north- and southward range expansion and establishment. However, with the threat of regional and global climate change the potential for further expansion becomes greater. It is therefore

important to develop an understanding of a species’ fundamental thermal niche to enable predictions of the possible effects (Pörtner and Knust 2007, Somero 2011, Diamond et al. 2012). Furthermore a good knowledge of the guppy’s thermal ecology is essential if environmental managers are to be able to mitigate any negative effects of present and future invasions (e.g. Laha and Mattingly 2006, Priddis et al. 2009, Warren et al. 2013).

Question

To predict the potential consequences of changes in thermal regime it is first necessary to investigate how species respond to ecologically relevant changes to the thermal environment (Somero 2011, Chown 2012, Diamond et al. 2012). Therefore, the question in which this thesis is interested is:

How do changing environmental conditions affect fitness-altering traits?

In the following five chapters I will describe the investigations I undertook in an effort to develop an enhanced understanding of the guppy’s thermal niche.

Chapter Two

Temperature and light both play a key role in controlling daily activity patterns as temperature has a direct effect on ectotherm metabolism and brighter conditions increases the possibility of being detected by predators. In wild fish, light has a proven effect on activity while temperature has been less studied. As temperature and light are so closely connected, in an attempt to disentangle the effects of light and temperature from time of day, I investigated the relative importance of each factor on patterns in male mating activity during different periods of the day. The prediction in this experiment was that mating attempts would be lowest when light and temperature at their highest (midday).

How does natural variability in abiotic conditions affect daily patterns of mating activity in wild fish?

Chapter Three

The temperature of water in natural systems is subject to short term variability through a variety of sources (e.g. rainfall, insolation, industrial water effluent). The breadth of temperatures that a species can withstand for short periods of exposure provides a measure of their thermal tolerance. To investigate the effects of short term thermal change I exposed individual guppies to a change in temperature over a broad thermal range. I then created thermal performance curves (TPCs) to

describe the effect on male mating activity. I hypothesised that the guppy’s thermal breadth would be similar to the water temperatures they experience in Trinidad.

What are the immediate effects of temperature change on mating behaviours?

Chapter Four

Whether organisms can respond to prolonged periods of thermal change without a drastic loss of performance depends upon their ability to acclimate to the novel temperature. The success of acclimation is therefore dependent on an individual’s phenotypic flexibility. To investigate the temperature range over which guppies can acclimate completely I created three thermal regimes and allowed male and female guppies to acclimate for over 60 days. I then recorded the effect on male mating activity, observed changes in reproductive output and measured growth parameters in offspring born during the acclimation period. My prediction was that guppies would successfully acclimate and thus display highest performance when tested in the temperatures in which they were acclimated.

How does thermal acclimation alter performance in mating behaviour, growth and offspring traits at different temperatures?

Undertaking investigations using stable temperatures removes a source of variability from the analysis however questions remain over the ecological

relevance of the results as organisms rarely experience stable temperatures in the wild. To investigate how temperature alters life history in environmentally

realistic thermal conditions, I created two thermal regimes that fluctuated over daily cycles similar to those of the guppy’s natural environment. With individually- housed fish I first recorded the effect of thermal regime on life history traits over two generations. Using the same experimental set-up I then investigated a number of traits linked to male reproductive success – mating behaviour, sperm length and body colouration. Based on theoretical predictions, I hypothesised that the warmer treatments would result in faster growth, smaller adult size, decreased offspring size, shorter sperm and less colour than the colder treatment.

What are the effects of environmentally-realistic fluctuating temperatures on life history traits?

What are the effects of environmentally-realistic fluctuating temperatures on sexually selected traits?

Aims

The aims of this thesis are to:

 Describe how natural variability in abiotic conditions affects daily patterns of mating activity in wild fish. Chapter Two

 Establish what the immediate effects of temperature change are on mating behaviours.Chapter Three

 Investigate how thermal acclimation alters performance in mating behaviour, growth and offspring traits at different temperatures.

Chapter Four

 Explore what the effects of environmentally-realistic fluctuating temperatures are:

o on growth and reproductive characteristics. Chapter Five o and on sexually selected traits. Chapter Six

Chapter two:

Interplay of temperature and light influences daily