The Cichlidae family display a variety of mating and parental care behaviour. This includes courtship rituals such as the unique behavioural trait of bower-building, monogamous and polygamous mating systems, and their association with parental care strategies. Other alternative mating techniques will also be discussed, such as stealth mating, floating, and piracy. In this review, the general mating and parental behaviours of cichlids will be covered, with an emphasis on cichlids in the Great Lakes of East Africa due to the rapid speciation and large number of research focused in the region. IntroductionCichlids (family Cichlidae) is a large, diverse family (~1650 species) of fish, which typically consist of three major clades: African, Indian and Neotropical (Friedman et al. , 2013). Cichlidae is considered to be one of the largest vertebrate family due to their rapid radiation and speciation, especially in the Great Lakes of East Africa. They are also susceptible to reproduction in a laboratory setting and to genetic analysis. Mating and parental care strategies are shaped by evolutionary mechanisms, which is why cichlids are considered as an ideal model system due to their incredible diversity in courtship rituals, mating systems, parental care strategies and alternative reproductive strategies, all of which would be briefly covered in this review.
Cichlid fish express a variety of courtship rituals, which are based on the detailed ethology collected by Baerends & Baerends van Roon (1950). They perform courtship rituals like tilting, leading, circling, tail-wagging and quivering. Jerking (head bent sideways at an angle and brought back, repeated from left to right), can be observed regularly among courtship of many cichlid fishes. Jerking merges into quivering (position becomes more vertical), in which their body waves become stronger and the tail is swept sideways violently. At higher intensity, the usually closed mouths of fish would open, thus the substrate the fish is facing will get taken up by their mouths.
For those sand-dwelling fishes, like Cichlasoma, quivering could thus lead to digging, as they take up sand into their mouths. Studies have shown that quivering in Tramitichromis intermedius correlated with acoustic signals produced.
This correlation was also seen in other cichlid species (Ripley & Lobel, 2004). Since quivering is specific to mating behaviour, sound production is likely to be intentional for mating behaviour given the correlation. Cichlid fishes also have a hierarchal system, where the dominant male has a brighter colour and larger size (Barlow & Ballin, 1976). Thus, there is a possibility that females may use cues from sound production to assess the quality of the male, with increasing sound production as dominance increases. it is important to note that sound production does not always accompany quivering – non-territorial males do not produce sound when quivering, while those which are territorial, produces sound. The number of sounds produced also increased as the spawning period drew closer, suggesting the importance of sound in mating signals (Ripley & Lobel, 2004).
There is a difference between digging and pit-building, as the former is irregular and aimless while the latter is methodical and localised. Pit-building is an example of bower building, which is a focal point of male courtship displays. Males of many sand-dwelling species (from Lake Malawi, Lake Victoria, Lake Tanganyika, etc) build elaborate and varied bowers, suggesting that the inclination to build castles or dig pits as a way to attract mates is the result of parallel evolution (York et al. , 2015). Cichlid bowers have at least ten forms, but the basic forms are: pits and castles. Streelman & Danley (2003) proposed a radiation-in-stages model where communication signals (inclusive of bower building) was possibly largely driven by sexual selection. For bower building species, two different behavioural phenotypes exist: 1) the dynamic courtship displays of the male, and 2) the bower itself. The variability of the two phenotypes are species-specific. For example, according to a study done by York et al (2015), Copadichromis virginalis seemed to spend more time displaying and less time constructing the bower compared to Mchenga conophoros, although not significantly different given the small sample size used.
Cichlid fishes are known to mate either monogamously or polygamously. Monogamous species are typically isomorphic (Darwin, 1871), although males tend to be larger than females (Thorson, 1976). Mating in monogamous species differs from polygamous (especially polygynous) species, mostly in the duration of interaction between males and females (Baylis, 1976). Monogamous pairs may spend weeks to years together, while polygynous pairs come together briefly (seconds to minutes) for spawning. There are three reasons for the lengthier duration in monogamous species. Firstly, sexual dimorphism help in the recognition of the opposite sex while the isomorphism may require more time to distinguish species and sex, thus the phenomenon of monogamous species spending more time together (Burley, 1981). Secondly, the readiness to mate might differ between monogamous and polygynous species.
For territorial polygynous fish, the male already has a breeding site where the receptive female would approach when spawning is near. For monogamous species, the pair formation happens before spawning, and the female might not be ready to spawn at that moment in time (Barlow, 1992). Lastly, the differential choosiness of females and males resulting in longer duration of interaction. Anisogamy predicts that females tend to be choosy while males are not. This can be seen in polygynous species where females tend to choose males which are of better quality. Monogamous (biparental) species, on the other hand, tend to be equally choosy especially when male care is paramount in offspring survival (Barlow, 1992). Biparental, monogamous pairs must cooperate with each other, and mutually defend their territories (offspring, food resources, shelter) from other conspecifics (Morley & Balshine, 2002). The pay-off to stay must outweigh the pay-off to desert their partner. It was suggested that in situations where an individual cannot defend territories by themselves (Morley & Balshine, 2002), lack of available partners due to low densities or skewed sex ratios (Nakai et al. , 1990), limited resources (food or breeding site), or large clutches of offspring (Kuwamura, 1986), monogamy is preferred.
Mating systems is closely related to the extent and type of parental care, as care-giving will affect the mating opportunities. In cichlid fishes, there are multiple strategies of parental care, such as mouthbrooding, uniparental (maternal or paternal) and cooperative. Substrate-brooding (guarding) is often associated with biparental monogamy. This is also a common behaviour for Asian and American cichlids (Breder & Rosen, 1966; Iles & Fryer, 1972). For mouthbrooding, cichlid species tend to be polygamous as breeding sites are safer (Keenleyside, 1991), and thus does not require two parents to defend the breeding territory together. This behaviour is largely seen in African cichlids (Iles & Fryer, 1972).
However, it must be kept in mind that the mating system of each cichlid species is not consistently correlated to its brooding system. Exceptions such as Haplotaxodon mierolepis (Kuwamura, 1986), Asprotilapia leptura (yaniagisawa, 1986), Aequidens paraguayensis (Timms & Keenleyside, 1975) are monogamous mouthbrooders, and cichlid species such as Lamprologus brichardi, L. fureifer and L. modestus are polygynous substrate brooders (Kuwamura, 1986). Cooperative breeding is also observed in several (19-21 species) Lake Tanganyikan cichlid species, where helper systems exist comprising dominant breeders and subordinate helpers (Heg & Bachar, 2006). Since there is a variety of helper systems, with different group sizes, helper-breeder relatedness, and direct helper reproduction, the benefits and costs of a cooperative breeding system vary as well. Most research on this parental care strategy were done on the Neolamprologus family, such as on brood care, mating systems, turnover rate of helpers and breeders, among others (Heg et al. , 2008; Schurch & Heg, 2010; Wong & Balshine, 2011).
Due to the plasticity of mating tactics, several alternative male mating strategies have been described. In cichlids (around 15 species), while territorial males recruit females into their spawning sites, non-territorial males may adopt different strategies, such as sneaking, floaters and piracy (McKaye, 1983; Tarborsky, 1984; Kuwamura, 1987). Sneaker males would take advantage of the courting activities by other males, to stealthily fertilise or eat the eggs in the spawning site. Floaters simply try to occupy recently emptied spawn sites. Pirates, on the other hand, are more aggressive as they take over the sites (not vacant) and have unrestricted access to the unfertilised eggs. Well studied examples include Lamprologus callipterus (shell breeder; Sato, 1994), Telmatochromis temporalis (hole breeder; Nakano & Nagoshi, 1990) and Telmatochromis vittatus (shell breeder, Ota & Kohda, 2006) – which can also be hypothesised that substrate breeders are more at risk to alternative mating techniques as described above.
Overall, there is a wealth of information regarding mating behaviour and parental care strategies of cichlid fishes through extensive field work and experimental research. These researches also address comparative and evolutionary questions as they show a huge diversity in courtship signals, mating systems and parental care strategies. However, the cichlid fish species of the Great Lakes in East Africa (Lake Victoria, Lake Malawi and Lake Tanganyika) are the most studied due to its rapid speciation and diversity, as compared to the species from Asia and South America – where our knowledge is lacking. Mate choice is an incredibly important aspect of mating behaviour, but not touched on in this review as it is often considered secondary in the evolution of cichlids, and therefore research regarding assortative mating is limited. These demonstrate that there is still need for further field and laboratory studies in a larger cichlid variety, as well as on male and female decision-making regarding mates, since it is crucial to understanding mating behaviour in cichlid fish species.
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