Or (c) interactively, where the two factors can contribute equally strong
Or (c) interactively, where the two factors can contribute equally strong to phenotypic change (upper panel) or one level of one factor masks the effect of the other factor by a compensatory response; see text for examples of each case.multiple Valsartan/sacubitril cost environmental factors in order to express adequate plastic responses during development [88]. For example, Daphnia magna required combined cues on current resource availability, photoperiod and population density in order to induce a switch from clonal reproduction to the production of sexual, dormant eggs, which can endure harsh conditions [77]. Additive effects of two factors become apparent by parallel reaction norms, but they can be interpreted in two ways; a second factor can be viewed to enhance the effect induced by a first factor (Fig. 3b, upper panel) or to reduce its effect (Fig. 3b, lower panel). The latter case may indicate that a trade-off is involved between the responses to both factors. An example of an enhancing effect is that the presence of early predator cues enhanced growth and thus final size in both low-food and high-food reared guppies [85]. An example of a trade-off is that anti-predator responses may have to be traded off against the development of morphological structures. In the absence of predation risk, wood frog tadpoles (Rana sylvatica) develop increasingly longer guts with increasing conspecific competition PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/28404814 [89]. The same positive relationship between gut length and competitor density was found if tadpoles were reared in different concentrations of predator cues, but the higher the perceived predation risk the shorter the gut length was across all densitytreatments. Instead, under predation risk tadpoles allocated resources more into tail development. Certainly the most interesting outcomes of designs with multiple environmental factors are interactive effects where reaction norms differ in slope. Most striking are examples where the slopes of reaction norms have opposite signs (Fig. 3c, upper panel). This was found, for example, when the influences of early social and predator experiences on the social behaviour of the cooperatively breeding cichlid N. pulcher were investigated. Different behavioural specializations in the social domain of the four treatment groups indicated that these fish required the information of both early environmental experiences to develop adequate behaviours [86], a fact that was overlooked when only the early social environment had been manipulated [28,76,90]. Unless full factorial experiments are employed, environmental effects may be entirely overlooked because they can be masked by a second factor. This can happen when one reaction norm has a slope different from zero and the other one is flat (Fig. 3c, lower panel). This has been demonstrated in crickets (Telogyllus commodus), in which a protein reduced diet resulted in the development of smaller adult size. These size differences vanished, however, when crickets were provided with acoustic cues signalling high future intra-sexualGroothuis and Taborsky Frontiers in Zoology 2015, 12(Suppl 1):S6 http://www.frontiersinzoology.com/content/12/S1/SPage 12 ofcompetition. By anticipating future competition, crickets enhanced growth during their last nymphal stage and were thereby able to compensate fully for initial grow deficits [91]. Interestingly, also the absence of an environmental trigger can have masking effects. Tail morphology of tadpoles is a textbook example of predator induced.