Atresia has been poorly examined in cephalopods. We here provide a histological 12 description of this process along the whole ovary development for Octopus vulgaris. 13 Additionally, we related its occurrence to morphometric parameters, and its seasonal 14 cycle was further analysed. Atresia occurred all year round in immature and mature 15 females and in previtellogenic and vitellogenic oocytes. However, more mature females 16 were more prone of being atretic. This occurred mainly in spring when females had 17 atretic previtellogenic oocytes in mature macrostages. By contrast, vitellogenic atresia 18 occurred mainly from spawning to post-spawning females. Furthermore, two types of 19 phagocytic cells were identified as responsible for the reabsorption during atresia. The 20 phagocytic follicle cells only occurred in yolk-bearing oocytes; and within the two 21 haemocyte populations only the smaller ones seemed to be involved in engulfing atretic 22 oocytes. Additionally, advanced atresia in post-spawning females showed yellow-brown 23 bodies as a possible result of follicle cell apoptosis and highlighting the end of the 24 reproductive cycle. Given the pattern of atresia, the reproductive strategy of this species 25 Manuscript Click here to download Manuscript Atresia O. vulgaris ZOOMORPHOLOGY.doc Click here to view linked References is based on an asynchronic ovary development and a synchronous ovulation during 26 spawning. We further suggest that potential fecundity for this species should be 27 measured on late vitellogenic oocytes in pre-spawning females. 28 35 external factors. Thus, since ovarian atresia affects fertility rates, its determination 36 allows to differentiate between potential and total fecundity and to identify at what stage 37 of sexual maturity fecundity is reduced (Boyle & Chevis, 1992). In the case of 38 iteroparous species such as fishes, defining atretic stages and the subsequent assignment 39 of females to different spawning status (e.g. active, inactive/immature) are of great 40 importance for later estimation of spawning biomass (Hunter & Macewicz, 1985; 41 Hunter & Lo, 1997). Moreover, the study of prevalence and intensity of histological 42 stages of the atretic oocytes allows predicting the cessation of spawning for a given 43 population (Kurita et al., 2003; Ganias et al., 2003). Furthermore, atresia is essential for 44 the maintenance of ovarian homeostasis; however, a number of factors have been 45 described as potential causes of increased ovarian atresia such as marine pollution or 46 reduced food supply (Cabrera-Páez et al., 2009; Ortiz-Zarragoitia et al., 2011; 47 Yamamoto et al., 2011). Thus, besides indicating a poorer physiological condition for 48 reproduction, elevated atretic indices could also reflect an environmental impact. 49 Gonadal atresia can appear at any stage of oocyte development; however, it is 50 mainly described in vitellogenic oocytes in both marine vertebrates and invertebrates. 51 By contrast, atresia in previtellogenic oocytes is less evident becaus...
