The results revealed a conspicuous kin recognition and avoidance of mating between the relatives in P. dissecta, which was greater in the mating partners of different generations, i.e. father-daughter and mother-son. The decrease in mating durations along with the subtle displays of female mating refusals indicate that females (both daughter and mother in sets B and C, respectively) tried to avoid this mating. This shows that the female ladybirds can differentiate between mating partners at the age-level and (i) refrain from mating with very younger or older mating partners, or (ii) identify their mating partners due to similar chemical signatures and avoid mating with relatives. Such mating has also reduced the duration of copula, which suggests both relatedness and age-disparity have negative effects. However, young females of P. dissecta paired with middle-aged males resulted in increased mating incidences with fitter progeny than when paired with younger males (Pervez et al. 2004). Contrarily, we didn’t find this in the father and daughter combination, as female was highly reluctant to copulate. It seems more likely that a female’s averseness to mate with her father attributes to avoidance of consanguineous mating. Yasui (1998) suggested that mating with new males can benefit the reproductive success of females in terms of healthier offspring and reduced risk of infection. It also seems plausible that high mating duration in unrelated mating partners indicates a simple acceptance of unrelated males by females to avoid inbreeding, as also supported by the decline in mating duration amongst relatives.
The mating duration between unrelated mates recorded in the present study is found to be greater than in the previous report (Omkar and Pervez, 2005). However, Pervez et al. (2004) demonstrated the quick responsiveness of males toward middle-aged female P. dissecta due to the high mating willingness of the female, as females when palpated became static which allowed mating. Similar behaviour of the males toward older and mature females was reported in A. bipunctata (Hemptinne et al. 2001). Contrarily, we found just the opposite behaviour due to the degree of relatedness between the mates with the lowest duration of copula between mother-son mating. Subsequently, prolonged mating between unrelated couples has a positive relationship with fecundity and percent egg viability. We knew sperm transfer is continuous throughout the copulation act in aphidophagous ladybirds, where sperm is not transferred via spermatophore (Omkar et al. 2006). Thus, mating duration is directly positively associated with the transfer of sperm load and storing them, which could be operational in fertilizing eggs in non-mating conditions. This explains why mating once for a longer mating duration could result in quantitative fertile fecundity. In ladybirds and other insect species, various seminal fluid proteins are known to be directly connected with the duration of mating (Engqvist et al. 2007; Liu et al. 2011). In addition, prolonged mating duration is beneficial for the male as it inhibits female re-mating, however it may elevate the cost of mating to females (Schofl and Taborsky, 2002). Nevertheless, the potential benefits gained by extended mating duration even after sperm transfer includes monopolization of mating partner for further clutches (Linn et al. 2007), sperm-loading (Weldingh et al. 2011), and mate-guarding (Chaudhary et al. 2015).
In the present study, a significant effect of male-female kinship is observed on reproductive attributes like immature survival, adult emergence and weight of larvae. The unrelated female was the most fecund with optimal immature survival, adult emergence, egg-weight, higher larvae and adult weights with enhanced fitness than other relative females. Similarly, females of the cabbage beetle, Colaphellus bowringi, that mated with siblings resulted in poor hatching success, longer development duration, lower immature survival and lower body mass of larvae than the females who mated with unrelated males suggesting inbreeding depression (Liu et al. 2014). In addition, C. bowringi females initially avoided mating with sibling males as a strategy of pre-copulatory inbreeding avoidance. Fox (2005) reported that eggs of bruchine beetle, Stator limbatus Horn, deposited after mating with a sibling male were less likely to develop with deteriorated immature survival rate. We found the offspring fitness of unrelated couples to be better than that of relatives, which was probably due to the reduced heterozygosity and inbreeding in the latter (Keller and Ross, 1998). The reduced fitness may even be detrimental to lesser resistance to diseases (Cassinello et al. 2001), and mating success (Acevedo-Whitehouse et al. 2003), which may further deteriorate the overall inclusive fitness (Reid et al. 2003). Insects do evolve mechanisms to avoid inbreeding with relatives (Ala-Honkola, 2011; Tabadkani et al. 2012; Saxena et al. 2016), as inbreeding may create negative effects on female fecundity (van Oosterhout et al. 2000; Roff and DeRose, 2001), egg viability (Armbruster et al. 2000), immature survival (Haikola, 2003), total development time (Morjan et al. 1999), body size (Roff, 2002), development stability (Reale and Roff, 2003), fertility (Saccheri et al. 2005), adult mating behavior (Joron and Brakefield, 2003), and adult lifespan (van Oosterhout et al. 2000). Despite evidence of inbreeding depression in numerous above studies on non-ladybird insects, little is known about the avoidance of mating with relatives due to inbreeding depressions in ladybirds. Our results raise a question on the process of mass-rearing, where the ladybirds are augmented giving no consideration to the parental line and allowing mating between relatives and thereby inviting inbreeding depression, which may gradually deteriorate the quality of progeny and making them less fit for the biocontrol programmes. Hence, to draw broader conclusions, further studies on this issue are needed to examine the negative effects of inbreeding during mass-multiplication techniques on the fitness of ladybirds.