Journal of Morphology

Hoover, R. C.; Heras, Joseph; Ford, Kassandra L.; Cohen, Karly E.; Donatelli, Cassandra M.

doi: 10.1002/jmor.70131pmid: N/A

Pricklebacks (Stichaeidae) are a useful model for studying dietary diversity in fishes. Several species integrate increasing amounts of plant material into their diets as they grow, which is matched by physiological adaptations and allometric growth of the digestive tract to enhance the digestion of plant material. Similar to physiological differences, there are varying mechanical demands of eating plants compared to a carnivorous diet; we hypothesize that oral jaw morphology, dental characteristics, and tooth functional variation reflect diverse diets in pricklebacks. To explore this relationship, we first captured high‐resolution jaw and dentition morphology using microCT scanning across four species of prickleback over ontogeny (n = 9 per species), and 3 outgroups (n = 3 per species). We compared traits between species and quantified the scaling of these traits over ontogeny. We then use linear discriminant analyses to identify traits that drive differences between dietary groups. Pricklebacks span a range of jaw and tooth morphotypes from large jaws with many villiform teeth, to short jaws with large, rounded teeth. While there is overlap between groups, we find several traits define dietary groups and diverge via allometry. However, comparison with outgroups reveals high morphological diversity within each dietary group.

doi: 10.1002/jmor.70128pmid: N/A

Tworzydlo, Waclaw; Sochaczewska, Magda; Bilinski, Szczepan M.

doi: 10.1002/jmor.70127pmid: N/A

Comparison of the detailed morphology of ovaries allows for an evolutionary conclusion in insects. The current study characterized the ovary/ovariole organization in both thysanopteran subtaxa (Terebrantia and Tubulifera) and confirmed the presence of a (putative) germ plasm in the oocytes. Using transmission and scanning electron microscopy as well as histological methods, we show that the morphology of ovaries in the studied terebrantians and tubuliferans differs in the organization of the anterior ovary/ovariole region, that is, the germaria and terminal filaments. Whereas in tubuliferan, Haplothrips leucanthemi, the terminal filaments and germaria of all four ovarioles constituting a given ovary form single common structures (a common terminal filament and a germarial chamber, respectively), in the analyzed terebrantians (Frankliniella occidentalis and Thrips sp.), they remain individual, as in all other insect orders. Thus, the fusion of the anterior ovariole parts is interpreted as an apomorphy characteristic of tubuliferan thrips only. In contrast, the course of oogenesis in terebrantians and tubuliferans is rather similar and reveals one prominent feature: the presence of a distinct nuage layer encompassing oocyte nuclei. We also show that after reinitiation of the first meiotic division in representatives of both thysanopteran subgroups, a small irregular region of cytoplasm arises at the posterior oocyte extremity. We suggest that this region is homologous to the germ plasm of holometabolous insects.

Ha, Myoung‐Hoon; Chapuis, Lucille; Dutka, Travis L.; Pepperell, Julian; Kerr, Caroline C.; Collin, Shaun P.

doi: 10.1002/jmor.70133pmid: N/A

Olfactory receptor neurons (ORNs) of teleosts interact with waterborne odorants and serve as a crucial first step in detecting and transmitting the olfactory signal to the brain. Despite the significance of olfaction in feeding among pelagic teleosts, very little is known about the spatial distribution pattern of the density and types of ORNs on the olfactory lamellar surface. A scanning electron microscopy (SEM) investigation was conducted on southern bluefin tuna, Thunnus maccoyii, to quantify the types and density of ORNs in different parts of the olfactory lamellar surface. SEM revealed two types of ORNs: ciliated olfactory receptor neurons (cORNs) and microvillous olfactory receptor neurons (mORNs). The cORNs are dominant over mORNs with mean densities of 84,000 mm−2 and 5000 mm−2, respectively. Ciliated non‐sensory cells (cNSs) are present at the periphery of the olfactory epithelium, with a mean density of 800 mm−2. The mORNs display a distinct, heterogeneous spatial distribution, being highly concentrated in the rostral region of the lamellar surface, especially at the entry of the interlamellar space. Based on the hydrodynamics of the incoming flow of seawater within the interlamellar spaces and the topography of the olfactory epithelium, the rostral distribution of mORNs is organised to optimise interactions with water‐borne stimuli. The mean density of ORNs on the lamellar surface of T. maccoyii (90,000 mm−2) is one of the highest among teleosts reported to date, which may serve as an anatomical indicator of high olfactory ability.

Duque‐Correa, M. J.; Meloro, C.; Keller, S.; Cigler, P.; Wethli, I.; Niehaus, J.; Przybyło, M.; Clauss, M.

doi: 10.1002/jmor.70130pmid: N/A

Across four large vertebrate groups—fish, reptiles, birds and mammals— intestine length has been shown to scale hyper‐allometrically with body mass (BM), at an exponent higher than the geometric (isometric) expectation, 0.33. So far, amphibians have not been investigated in this respect. Combining original data from dissections and literature data, we evaluated the scaling of total intestine length with BM in the adult stages of 38 amphibian species (37 of which anurans). The BM range of investigated taxa was 2.2 to 113.5 g. When accounting for phylogeny, intestine length scaled with BM at an exponent with a 95% confidence interval of 0.39 to 0.53, corroborating the hyper‐allometric scaling observed in other vertebrates. The hypothetical explanation is that larger animals, while requiring a proportionate intestinal absorptive surface to meet their metabolic demands, need to maintain short diffusion distances between the sites of digestive enzyme secretion/nutrient absorption and the digesta. This mechanism should result in hypo‐allometric scaling of intestine diameter, with the hyper‐allometric scaling of intestinal length ensuring the overall constancy of functional organ surface.

Peña‐Cutimbo, Nelly; Segura‐Cobeña, Eduardo; Cañedo‐Apolaya, Rosa Maria; Mangel, Jeffrey C.; Alfaro‐Shigueto, Joanna

doi: 10.1002/jmor.70134pmid: N/A

Extensive fishing has caused a significant decline in the populations of the Chilean angelshark Squatina armata, yet limited information on the basic biology of the species presents an obstacle for science‐based conservation and management policies. Here, we present a morphometric analysis of the reproductive system of S. armata. Seventy‐six specimens were collected from the artisanal fisheries using bottom gillnets and trammel nets, targeting mainly elasmobranchs. We determined sex, total length, and external characteristics such as the presence or absence of semen, rotation of the gonopterygia, opening of the rhyphiodon, thorns on the pectoral fins of males, and mating scars on females. Paired t‐tests and regression analyses were used to evaluate bilateral asymmetry in reproductive organs and the relationship between organ dimensions and total length. The analyses revealed directional asymmetry in both sexes, with the left ovary and uterus in females, and the left testis and epididymis in males, generally larger than the right counterparts. In addition, reproductive organ size increased significantly with total length. These results provide the first detailed description of reproductive organ morphology and asymmetry in S. armata, improving current knowledge of its reproductive development and providing baseline information for future reproductive and fisheries management studies.

Barrantes, Gilbert; Zúñiga‐Madrigal, Jorge; Cambronero‐Ulloa, Gustavo; Sánchez‐Quirós, Catalina; Sandoval, Luis; Madrigal‐Brenes, Ruth

doi: 10.1002/jmor.70132pmid: N/A

In adult spiders, leg lengths vary within and between species and is associated with functions in web construction, sensory activities, and prey capture. However, little is known about how leg proportions change during ontogeny. Here we investigate whether leg length relative to body size is maintained throughout development in three cobweb spiders (Latrodectus geometricus, L. mactans, and Steatoda grossa). Because spiderlings of these species build webs and capture prey from the first instar, we predicted proportional growth across instars. We also evaluate which model (linear, quadratic, or Gompertz) best describes femur and tibia growth, and estimated growth rates (first derivative) and accelerations (second derivative) for each sex and species. Legs were proportionally shorter in early than in later instars in L. geometricus and S. grossa, whereas proportions remained similar across development in L. mactans. Femur and tibia growth was best described by a quadratic model in both sexes of L. geometricus and L. mactans, and in males of S. grossa. In contrast, females of S. grossa followed a Gompertz trajectory; with high early growth rates that declined toward maturity. Despite these differences in trajectories, leg segments showed similar magnitudes of acceleration within species. Across the three theridiid species, females showed two distinct ontogenetic patterns–steady increases in growth rate (quadratic) or rapid early growth followed by deceleration (Gompertz)–whereas males consistently followed quadratic trajectories. Conserved acceleration among leg segments may reflect developmental canalization that preserves functional proportionality during growth.

Giacchino, Mariela; Inserra, Pablo I. F.; Claver, Juan A.; Gariboldi, María C; Lange, Fernando D.; Ferraris, Sergio R.; Leopardo, Noelia P.; Vitullo, Alfredo D.

doi: 10.1002/jmor.70129pmid: N/A

The male genital morphology of the plains vizcacha (Lagostomus maximus) remains poorly characterized despite the species' distinctive reproductive biology and its phylogenetic position within Caviomorpha. In this study, we describe the gross anatomy, histology, and ultrastructure of the penis of L. maximus using light microscopy and scanning electron microscopy. The genitalia of the vizcacha shares several features with other caviomorph rodents, including the absence of a pendulous scrotum, subcutaneous inguinal testes, and a retracted inverted S‐shaped penile configuration. Notably, we identify a previously undescribed narrow stylet‐like distal process supported by hyaline cartilage and bearing caudally oriented surface spine‐like projections, representing a novel morphological specialization among caviomorph rodents. These distal specializations may influence copulatory mechanics by enhancing mechanical stimulation of the female reproductive tract. When considered alongside recent evidence suggesting a mixed ovulatory strategy in L. maximus, including a seminal plasma–induced ovulatory process, these findings raise the possibility that penile morphology contributes synergistically to ovulation induction. Our results expand current knowledge of genital diversity in caviomorph rodents and provide a morphological framework for future functional and evolutionary investigations.