Evidence for neither the compensation hypothesis nor the expensive-tissue hypothesis in Carassius auratus

Abstract

In many taxa, the left and right testes often differ in size. The compensation hypothesis states that an increase in size of one tesüs can compensate for a reduced function in the other testis. Moreover, the expensive-tissue hypothesis predicts that an increase in investment of a metabolically costly tissue is offset by decreasing investment in the other metaboUcally costly tissues. Here we tested these two hypotheses in Carassius auratus, by analysing difference between left and right testes mass, and between brain mass and both gut length and gonad mass (testes mass in males and clutch mass in females). We found no difference between left and right testis mass and no correlations between relative testis size and body measurements. These findings suggest that the left testis cannot serve a compensatory role. Nonetheless, contrary to the predictions of the expensive-tissue hypothesis, brain mass was positively correlated with both gut length and gonad mass within each sex. This positive correlation between brain mass and other organs (gut, gonad and clutch tissues) suggests that organisms may compensate for substantial variation in investment in tissues without sacrificing other expensive tissues.

Brain size evolution in the frog Fejervarya limnocharis supports neither the cognitive buffer nor the expensive brain hypothesis

“…For anurans, variation in absolute brain size can be strongly affected environmentally (Gonda et al ., ; Jiang et al ., ). Absolute brain size has been proposed to account for differences in behavioral abilities among animals (Reader & Laland, ; Yopak et al ., ; Gonda et al ., ; Liu, Zhou & Liao, ; Jin et al ., ; Tsuboi et al ., ; Zeng et al ., ). We found a significant population variation in absolute brain volume for both sexes, suggesting that the differences in brain morphology between habitats are results of drift without any selection acting on them.…”

Testing ontogenetic patterns of sexual size dimorphism against expectations of the expensive tissue hypothesis, an intraspecific example using oyster toadfish (Opsanus tau)

“…Tests for investment trade‐offs expected under the ETH have repeatedly focused on the heart, brain, and liver as candidate organs (e.g., Aiello, ; Navarrete et al., ; Warren & Iglesias, ), as these are metabolically expensive and likely subjected to evolutionary trade‐offs (Konarzewski & Diamond, ). Since the inception of the ETH, several studies have also expanded the candidate pool of potential metabolically expensive organs subjected to trade‐offs to include gonads (e.g., Bordes et al., ; Liu, Zhou, & Liao, ; Tsuboi, Shoji, Sogabe, Ahnesjö, & Kolm, ). As such our study captures tissues generally considered to be among the most likely targets for metabolic trade‐offs.…”

The Expensive-Tissue Hypothesis in Vertebrates: Gut Microbiota Effect, a Review

“…The expensive-tissue hypothesis (ETH), with regard to vertebrate evolution, states that the metabolic requirement of a relatively large brain should be compensated for by a reduction in the size of the gut, which is also an energetically costly organ, and other costly tissues [ 15 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ]. In addition to evidence for the ETH, there have also been studies with results that refuted the theory [ 43 , 44 , 45 , 46 , 47 , 49 ]. Since its original formulation there have been extensions to the hypothesis, however, the “energy trade-off hypothesis” is one of the proposed extensions of the original ETH [ 44 ] that suggests that the cost of increased brain size can be compensated by a costly loss of traits including and other than gut size and digestion, such as body maintenance [ 45 ], locomotion [ 47 ], development [ 46 ], and reproduction [ 43 , 49 ].…”

“…The Expensive-Tissue Hypothesis (ETH) states that the high energetic expenditure of larger brains requires a matching decrease in other energetic-consuming organisms (e.g., guts) [ 15 , 36 , 37 , 38 , 39 , 41 , 42 ]. However, studies have refuted the ETH [ 43 , 44 , 45 , 46 , 47 ] and proposed the trade-off hypothesis, which suggests that instead of tissue investment, a series of trade-offs with other energetically costly traits such as body maintenance, locomotion, development, and reproductive investment (e.g., testes mass) can compensate for the cost of increased brain size [ 39 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. Nonetheless, the gut plays an important role in brain size evolution and can be viewed as one of these energy trade-offs.…”