Girdle Structure Research Articles

Girdle Band Structure in the Diatom Genus Proschkinia (Bacillariophyta)—Another Potential Adaptation to Stabilise a Deep Cingulum?

The girdle structure of Proschkinia (Bacillariophyta) is described in detail, showing the form of the unusual, channelled bands and how they link together. The significance and potential function of the more complex band structure is discussed in relation to its occurrence in other diatom genera and to other potential stabilising elements. Although some similarities in girdle structure are seen with the diatom genus Undatella, there is currently no evidence of a close phylogenetic relationship between these genera. Based on the current molecular data, Proschkinia is most closely related to the genus Fistulifera, with which it shares a distinctive valve feature, a fistula. Because of the traditional focus on valve morphology, far less is known of the girdle structure within the diatoms, despite its importance for maintaining cell integrity and allowing cell growth. The importance of studying the girdle structure as well as the valve morphology in diatoms in relation to their phylogeny and ecology is stressed.

Nitzschia captiva sp. nov. (Bacillariophyta), the essential prey diatom of the kleptoplastic dinoflagellate Durinskia capensis, compared with N. agnita, N. kuetzingioides and other species

ABSTRACT Durinskia capensis is a kleptoplastic dinoflagellate species from high intertidal marine rock pools, which can use a variety of diatoms for photosynthesis. However, very few of the diatoms permit indefinite survival of the dinoflagellate and rbcL sequences show that D. capensis isolated from nature contains one of two closely related Nitzschia species as its kleptoplastids. In culture, without a supply of these ‘essential’ Nitzschia cells to replenish the intracellular store of diatom plastids and other organelles, D. capensis eventually loses all its kleptoplastids and dies. Inside Durinskia, diatoms do not possess frustules and so cannot be compared morphologically with free-living forms. Recently, one of the essential Nitzschia species was isolated from the type locality of D. capensis and grown in culture, allowing comparison with similar Nitzschia species, particularly N. agnita and N. kuetzingioides, examined from type material. We conclude that the ‘essential diatom’ of D. capensis differs morphologically from these and other Nitzschia species and it is therefore described as N. captiva sp. nov. Nitzschia agnita and N. kuetzingioides, on the other hand, are conspecific and N. agnita has priority. Nitzschia captiva and N. agnita are extremely similar in valve shape, dimensions, pattern and ultrastructure, but can be separated by their girdle structure. Nitzschia agnita appears to be a freshwater species, though somewhat salt-tolerant. In contrast, N. captiva, which is known principally from records of the kleptoplastids of D. capensis rather than from frustules, is so far marine.

Understanding the Female Physical Examination in Patients with Chronic Pelvic and Perineal Pain.

(1) Background: The objective was to compare the exploration of chronic pelvic pain syndrome (CPPS) patients in different locations and establish the role of physical examination in CPPS patients. (2) Methods: We reviewed clinical data from 107 female patients with CPPS unresponsive to conventional therapies at Puerta de Hierro University Hospital Madrid, Spain, from May 2018 to June 2022. Patients were classified into three groups: (a) pelvic pain; (b) anorectal pain; or (c) vulvar/perineal pain. (3) Results: Although the demographics of patients with CPPS were different, their physical examinations were strikingly similar. Our study observed a comorbidity rate of 36% and 79% of central sensitization of pain. Seventy-one percent of patients had vulvar allodynia/hyperalgesia. Pain on examination was identified in any pelvic floor muscle, in any pelvic girdle structure, and neuropathic pain in 98%, 96%, and 89%, respectively. Patients with vulvar and perineal pain were more different from the other groups; these patients were younger and had fewer comorbidities and less central sensitization, less anorectal pain, more pain during intercourse, and greater nulliparity (p = 0.022; p = 0.040; p = 0.048; p = 0.000; p = 0.006; p = 0.005). (4) Conclusions: The findings of this study are related to the understanding of the pathophysiology of CPPS. The physical examination confirms the central sensitization of female patients with CPPS, helps us to determine the therapeutic management of the patient, and can be considered as a prognostic factor of the disease.

Transfer of the Antarctic diatom Nitzschia barbieri (Bacillariophyta) to the genus Fragilariopsis and emended descriptions of F. barbieri comb. nov. and F. peragallii

Fragilariopsis is a marine diatom genus that has a critical ecological role in Antarctic waters due to its high abundance and ubiquity in plankton and sea ice. Several species of Fragilariopsis are used extensively in paleoceanography due to their good preservation in marine sediments. Detailed morphological studies on Fragilariopsis species from Antarctic water and ice samples were thus performed. Nevertheless, some species of this genus still remain poorly studied. Based on close morphological similarity between the valve structure of the Antarctic diatom Nitzschia barbieri and the genus Fragilariopsis, we propose transferring N. barbieri to Fragilariopsis as Fragilariopsis barbieri comb. nov. The description of the two rarely reported species, F. barbieri and F. peragallii, were emended. The girdle structure and the formation of doublets in F. barbieri and F. peragallii are described and illustrated for the first time. The analyses were carried out by light and electron microscopy and complete the morphological description of the fourteen known extant taxa of Fragilariopsis from Antarctica. Relative abundance of Fragilariopsis species from sea ice is also presented.

Nitzschia fenestralis: A new diatom species abundant in the Holocene sediments of an eastern African crater lake

Nitzschia is common in the phytoplankton of several East African lakes. A new species, Nitzschia fenestralis, sp. nov. D. Grady, D.G. Mann et Trobajo was encountered at numerous depths in a 16 m sediment core from Lake Babogaya, Ethiopia and is described using light and scanning electron microscopy. It is compared with several other morphologically similar taxa described from East and Central Africa (especially N. aequalis, N. mediocris, N. obsoleta and N. fabiennejansseniana), and from Europe (N. fruticosa). An unusual feature of some of these species (N. fenestralis, N. obsoleta and N. fabiennejansseniana) is that in the raphe canal each stria is represented by two narrower areolae (alternatively interpreted as a single subdivided areola). It is this feature that suggested the name of the new species (through the resemblance to a series of sash windows). Another characteristic of N. fenestralis and N. obsoleta, apparently never reported previously in any diatom, is that the more advalvar bands end approximately halfway along the frustules, rather than at the poles. In most respects (shape and size, stria and fibula densities, valve and girdle structure), N. fenestralis and N. obsoleta are very similar, but confusion is unlikely because they differ in whether central raphe endings are present (N. fenestralis) or absent (N. obsoleta). In Nitzschia fenestralis, and perhaps to a lesser extent in N. obsoleta, the striae usually become strongly radiate towards the poles. A preliminary assessment, based on the literature, suggests that N. fabiennejansseniana may be synonymous with N. obsoleta, which was described earlier.

Diatomella colonialis, a new diatom species (Bacillariophyta) from the sub-Antarctic Region

During a survey of the freshwater diatom flora of the sub-Antarctic Kerguelen archipelago in the southern Indian Ocean, an unknown Diatomella taxon was observed forming long colonies using linking spines. Detailed morphological analysis based on light and scanning electron microscopical observations and comparison with all known Diatomella taxa worldwide justified the description of this unknown taxon as a new species: Diatomella colonialis sp. nov. The new taxon is characterized by the presence of marginal linking spines, the reduction of its raphe structure leaving only two short raphe slits near the apices, a very large axial area occupying almost the entire valve face and very short alveolate striae composed of paired areolae. The presence of these alveolate striae and the girdle structure with its typical scalariform valvocopula place this taxon in the genus Diatomella. The new species is described and compared with other Diatomella taxa. Notes on its distribution and ecology are added.

“Gyracanthus”sherwoodi(Gnathostomata, Gyracanthidae) from the Late Devonian of North America

New fossils of “Gyracanthus” sherwoodi Newberry, 1889 are described primarily from the Late Devonian Red Hill site and Metzger's Quarry (Catskill Formation, late Famennian) of Clinton and Sullivan Counties in central Pennsylvania. The fossils include ornamented prepectoral ventral plates, pectoral, pelvic, and dorsal fin spines, elements of the endoskeletal shoulder girdle (procoracoid and scapulocoracoid), scales, and possible anal fin spines. We distinguish between anterior and posterior dorsal fin spines. A growth series of elements, described for the first time for a gyracanth, show that the adults of this taxon reached about a meter in length, and juveniles already had ossified endoskeletal pectoral elements at body lengths 300–400 mm. The mainly cartilaginous skeleton, paired fin spines, shoulder girdle structure, and scale growth are consistent with gyracanthids being stem chondrichthyans. “Gyracanthus” sherwoodi lived in non-marine conditions in the eastern Laurentian rivers and deltas.

Probable mechanism of organic pores evolution in shale: Case study in Dalong Formation, Lower Yangtze area, China

Organic pores structures and their probable evolution mechanisms were analyzed by an Ar-ion milling (SEM) after a thermal simulation experiment. Several kinds of organic pores including girdle pores, circular pores, and spongy pores appeared during the thermal simulation process. The result shows that there are different possible mechanisms in organic pores evolution. Girdle pore is a typical pore structure in a particular period of hydrocarbons generation, and the girdle structure is an organic matter–mineral complex where the hydrocarbons generate. This phenomenon made it possible to observe the organic matter–mineral complex for the first time.

Chelonicola and Poulinea, two new gomphonemoid diatom genera (Bacillariophyta) living on marine turtles from Costa Rica

Marine mammals such as whales and dolphins have been known for a long time to host a very specific epizoic community on their skin. Less known however is the presence of a similar community on the carapaces of sea turtles. The present study is the first describing new taxa inhabiting sea turtle carapaces. Samples, collected from nesting olive ridley sea turtles (Lepidochelys olivacea) on Ostional Beach (Costa Rica), were studied using light and scanning electron microscopy. Two unknown small-celled gomphonemoid taxa were analysed in more detail and are described as two new genera, closely related to other gomphonemoid genera with septate girdle bands, such as Tripterion, Cuneolus and Gomphoseptatum. Chelonicola Majewska, De Stefano & Van de Vijver gen. nov. has a flat valve face, uniseriate striae composed of more than three areolae, simple external raphe endings, internally a siliceous flap over the proximal raphe endings and lives on mucilaginous stalks. Poulinea Majewska, De Stefano & Van de Vijver gen. nov. has at least one concave valve, uniseriate striae composed of only two elongated areolae, external distal raphe endings covered by thickened siliceous flaps and lives attached to the substrate by a mucilaginous pad. Chelonicola costaricensis Majewska, De Stefano & Van de Vijver sp. nov. and Poulinea lepidochelicola Majewska, De Stefano & Van de Vijver sp. nov. can be separated based on stria structure, girdle structure composed of more than 10 copulae, raphe structure and general valve outline. A cladistics analysis of putative members of the Rhoicospheniaceae indicates that the family is polyphyletic. Chelonicola and Poulinea are sister taxa, and form a monophyletic group with Cuneolus and Tripterion, but are not closely related to Rhoicosphenia, or other genera previously assigned to this family. Features used to help diagnose the family such as symmetry and presence of septa and pseudosepta are homoplastic across the raphid diatom tree of life.

Revision and phylogeny of narrow-mouthed treefrogs (Cophyla) from northern Madagascar: integration of molecular, osteological, and bioacoustic data reveals three new species.

We provide a revision of microhylid treefrogs of the genus Cophyla, the type genus of the subfamily Cophylinae. A phylogeny inferred from DNA sequences of multiple mitochondrial and nuclear genes, with representatives of all cophyline genera except Madecassophryne and including representatives of the two most divergent intrageneric lineages within Cophyla, placed Cophyla as sister group of Platypelis and confirmed both genera as reciprocally monophyletic. We describe three new Cophyla species based on osteological, morphological and bioacoustic characters as well as genetic differentiation in one nuclear and several mitochondrial markers. As in the vast majority of cophylines, all species of Cophyla emit long, stereotyped repetitions of a single tonal note, and we here consider one of these notes as a call; call duration thus equals note duration and the intervals between calls are named inter-call intervals. Cophyla maharipeo sp. nov. collected in Joffreville and Forêt d'Ambre Special Reserve (adult SVL 22-27 mm) is characterized by having long calls (1166-1346 ms) with long inter-call intervals (2154-3881 ms). Cophyla noromalalae sp. nov. collected in Montagne d'Ambre National Park (adult SVL 22-29 mm) is characterized by having short calls (662-821 ms) and short inter-call intervals (874-1882 ms). Cophyla puellarum sp. nov., also from Montagne d'Ambre National Park, is larger than the other two species (adult SVL 27.3-33.6 mm) and characterized by the shortest calls (326-390 ms) and long inter-call intervals (1961-3996 ms). Osteological analyses based on micro-CT scans and cleared and stained specimens confirms that the shape of the posterior vomer (centrally divided vs. undivided) may be a useful character to diagnose most species as belonging to either Platypelis and Cophyla, and suggest the absence of clavicles (present in Platypelis) is a derived character of most Cophyla. However, clavicles were present in C. puellarum, the only known Cophyla occurring at relatively high elevations (1250-1300 m a.s.l.) while otherwise in northern Madagascar, forests at higher elevations up to 2700 m a.s.l. are occupied by Platypelis species. Cophyla maharipeo was found at relatively low elevations (630-720 m a.s.l.), similar to the three previously known congeners (C. berara, C. occultans, C. phyllodactyla). Cophyla noromalalae occurs at intermediate elevations (900-1050 m a.s.l.). The molecular phylogeny inferred herein suggests that the ancestor of a clade containing all Cophyla species except C. puellarum evolved a modified shoulder girdle structure without ossified clavicles, and adapted to low-elevation habitats.

SCALY INCUNABULA, AUXOSPORE DEVELOPMENT, AND GIRDLE POLYMORPHISM IN SELLAPHORA MARVANII SP. NOV. (BACILLARIOPHYCEAE)(1).

Uniparental auxosporulation was observed in a monoclonal culture of a Sellaphora clone isolated from the epipelon of a fishpond in the Czech Republic. The cox1 sequence for the clone confirmed that it belonged to the Sellaphora pupula-bacillum species complex but showed significant differences from all previously characterized Sellaphora species, and it is therefore described as S. marvanii sp. nov. Protoplast, valve, and girdle structure resembled those of other Sellaphora species, but a novel finding for all diatoms was a change in girdle structure during the life cycle: the most advalvar girdle band (valvocopula) bore a single line of pores in enlarged postauxospore cells but was entirely plain in small cells and gametangia. The young auxospores were covered by incunabula containing large, delicate, ± circular scales, resembling those of centric diatom auxospores; similar scales have been reported in a few other raphid diatoms (Pseudo-nitzschia multiseries, Diploneis sp.) but contrast with the strip incunabula of some Nitzschia and Pinnularia and the helmet-like caps of Neidium. The scales persisted during auxospore expansion, mostly as two caps over the auxospore poles. The transverse perizonium comprised a very wide, closed primary band, flanked by numerous secondary bands whose open ends were strongly incurved toward the center. Initial valves were differentiated from their immediate descendants by the very strong external demarcation of the raphe sternum, irregular shape, and curved transapical profile.

Revision of the genus Hantzschia (Bacillariophyceae) on Livingston Island (South Shetland Islands, Southern Atlantic Ocean)

Diatoms (Bacillariophyta) are one of the most abundant groups of micro-algae present in the Antarctic Region, both in terms of number of species and of number of individuals (Jones 1996, Van de Vijver & Beyens 1999). The past ten years, the taxonomy of the Antarctic non-marine diatom flora has been thoroughly revised resulting in the description of a large number of new species (a.o. Van de Vijver et al. 2002, Van de Vijver & Mataloni 2008, Van de Vijver et al. 2010). An important part of these revisions focused on the typical terrestrial genera Luticola, Muelleria and Diadesmis. This is not surprising since one of the principal biomes in the Antarctic Region is formed by large, terrestrial ice-free areas, fellfields, wet soils, seepage areas and rocks. The soils of these areas form a suitable habitat for a large variety of terrestrial diatoms. Diatoms living in these habitats are welladapted to survive the sometimes severe conditions such as a continuously changing soil humidity and freeze-thaw cycles. Apart from the above-mentioned (already revised) genera, two other terrestrial genera form large populations within the Antarctic Region: Eunotia and Hantzschia. The present paper revises the taxonomy of the genus Hantzschia, based on observations made during a survey of the non-marine diatom flora of Livingston Island. Several unknown Hantzschia species were observed, that could not be assigned to any of the already described taxa. Five taxa will be described as new to science whereas three others are illustrated. The genus Hantzschia is a relatively small genus with less than fifty species known worldwide, occurring in a wide variety of habitats ranging from freshwater to terrestrial and even intertidal and marine environments (Round et al. 1990). Described in 1877 by Grunow, the genus, belonging to the family Bacillariaceae, is characterized by a typical asymmetrical valve outline with usually a more convex dorsal side and a concave ventral side, the presence of uniseriate striae composed of small rounded areolae containing hymenes, a raphe that is subtended by fibulae and a complex girdle structure (Round et al. 1990). Species within the genus are separated based on number of striae and areolae per stria, the position and shape of the fibulae, the shape of the external and internal proximal raphe endings and the shape of the valve apices. Hantzschia amphioxys (Ehrenb.) Grunow is considered to be the most common and well known species in this genus, living almost exclusively in (semi-wet) soils. The spe-

The phylogeny and classification of post-Palaeozoic echinoids

The relationships of post-Palaeozoic echinoids at family level are established through phylogenetic analysis of 169 taxa and 306 skeletal characters (excluding pedicellariae). Previous phylogenetic analyses of echinoids have either examined specific subgroups in detail or have looked at a relatively small number of taxa selected from across the class, with sparse sampling potentially affecting the reliability of results adversely. Our new analyses represent a compromise between encompassing the diversity of form that exists, while keeping the number of taxa to a level that does not make rigorous analysis impossibly time-consuming. In constructing the taxon-character data matrix we have encountered a surprising lack of primary data on plating pattern, lantern, and girdle structure for many supposedly “well-known” taxa. A well-resolved phylogenetic hypothesis was obtained and is used as the basis for a formal classification. Characters generally have a high retention index (>0.7) but low consistency index (<0.25) suggesting that, although characters are largely retained after they first evolve, most also undergo occasional reversal or convergence. Although parts of the resulting trees are only weakly supported (e.g. the precise sister group of the Irregularia), other parts are unambiguously resolved. Not unexpectedly, deep nodes are often not supported by unique apomorphies and higher taxa acquire their characteristic set of features over time. Diagnoses based on crown group taxa thus often fail to encompass fossil stem-group members adequately. Establishing the relationships of taxa at the root of large groups is hampered by limited character resolution. The influence of fossil taxa on the topology was explored by comparing the tree topologies obtained with and without their inclusion. We show that removal of fossils from stem groups makes no difference where their crown group is morphologically conservative, but has a major influence where extant sister groups are separated by large morphological gaps. Completeness of the echinoid record and its match to the stratigraphical record of first occurrences is tested using various metrics and found to be highly congruent, with irregular echinoids showing a higher congruence than regular ones.

Application of a continuum-mechanical model for the flow of anisotropic polar ice to the EDML core, Antarctica

AbstractWe present an application of the newly developed CAFFE model (Continuum-mechanical, Anisotropic Flow model based on an anisotropic Flow Enhancement factor) to the EPICA ice core at Kohnen Station, Dronning Maud Land, Antarctica (referred to as the EDML core). A one-dimensional flow model for the site is devised, which includes the anisotropic flow law and the fabric evolution equation of the CAFFE model. Three different solution methods are employed: (1) computing the ice flow based on the flow law of the CAFFE model and the measured fabrics; (2) solving the CAFFE fabric evolution equation under the simplifying assumption of transverse isotropy; and (3) solving the unrestricted CAFFE fabric evolution equation. Method (1) demonstrates clearly the importance of the anisotropic fabric in the ice column for the flow velocity. The anisotropic enhancement factor produced with method (2) agrees reasonably well with that of method (1), even though the measured fabric shows a girdle structure (which breaks the transverse isotropy) in large parts of the ice core. For method (3), we find that the measured fabric is reproduced well by the model down to ∼2100 m depth. Systematic deviations at greater depths are attributed to the disregard of migration recrystallization in the model.

Attheya ussurensis sp. nov. (Bacillariophyta)—a new marine diatom from the coastal waters of the Sea of Japan and a reappraisal of the genus

I.V. Stonik, T.Yu. Orlova and R.M. Crawford. 2006. Attheya ussurensis sp. nov. (Bacillariophyta)—a new marine diatom from the coastal waters of the Sea of Japan and a reappraisal of the genus. Phycologia 45: 141–147. DOI: 10.2216/04-48.1A new species of the mainly sand-dwelling marine diatom genus Attheya is described from the Sea of Japan. Of the seven species of the genus, Attheya ussurensis most closely resembles Attheya decora in its valve and girdle structure and in its plastid form and number, but it also possesses features found in one or other of the remaining species (presence of a rimoportula, pores in the girdle bands and horn morphology). Keys are provided to aid ide.gification of all known Attheya species.

Low sodium dodecyl sulfate concentrations inhibit tobacco mosaic virus coat protein amorphous aggregation and change the protein stability

Effects of low SDS concentrations on amorphous aggregation of tobacco mosaic virus (TMV) coat protein (CP) at 52 degrees C and on the protein structure were studied. It was found that SDS completely inhibits the TMV CP (11.5 microM) unordered aggregation at the detergent/CP molar ratio of 15 : 1 (0.005% SDS). As judged by fluorescence spectroscopy, these SDS concentrations did not prevent heating-induced disordering of the large-distance part of the TMV CP subunit, including the so-called "hydrophobic girdle". At somewhat higher SDS/protein ratio (40 : 1) the detergent completely disrupted the TMV CP hydrophobic girdle structure even at room temperature. At the same time, these low SDS concentrations (15 : 1, 40 : 1) strongly stabilized the structure of the small-distance part of the TMV CP molecule (the four alpha-helix bundle) against thermal disordering as judged by the far-UV (200-250 nm) CD spectra. Possible mechanisms of TMV CP heating-induced unordered aggregation initiation are discussed.

Two new species of snailfish genus Paraliparis (Pisces: Liparidae) from the Ross Sea, Antarctica

Two new species of Liparidae (snailfish) Paraliparis macrocephalus sp. nov. and P. rossi sp. nov., captured in the south‐western Ross Sea, Antarctica (74–75° S; 165–171° E), are described and illustrated. Paraliparis macrocephalus resembles, but is distinct from P. hubbsi, P. valentinae, P. somovi and P. aspersus. Paraliparis rossi is similar to P. macrocephalus in meristic counts, pectoral girdle structure and morphometry but differs in size of cephalic pores and nostril, shape of teeth, colour and other characters. Paraliparis macrocephalus was captured in the deepest locality in the Ross Sea, the Drygalski Trough, a 1200 m deep inner‐shelf depression. As trawling was preceded by video camera tows, a description of the substratum and fauna of these little‐studied trough habitats is also provided.

THE SYSTEMATICS OFSTAURONEIS(BACILLARIOPHYTA) II. THE LIFE HISTORY OFS. PHOENICENTERONAND RELATED SPECIES

Stauroneis phoenicenteron, the type species of Stauroneis, Stauroneis anceps (two moiphotypes) and S. legumen have Geitler's type IC auxosporulation, which has been demonstrated previously also in S. anceps var. siberica. Type IC auxosporulation is possessed by raphid diatoms with quite different valve, girdle and protoplast structure. This, coupled with the variation that occurs between type IC diatoms in, for example, the structure of the copulation envelope, auxospore shape, and the structure of the caps present at the ends of the auxospores, suggests that type IC auxosporulation is not in itself a reliable indicator of close systematic relationship. However, the particular kind of type IC auxosporulation found in Stauroneis also occurs in Craticula and “Navicula” protracta (but not in Navicula sensu stricto). All available evidence, from cell wall and protoplast characters, is consistent with the idea of a close relationship between these taxa and with the idea that the freshwater Stauroneis species b...

Tooth structure and phylogeny of the Upper Permian echinoid Miocidaris keyserlingi

SUMMARY Miocidaris keyserlingi is found in the Upper Permian Ford Formation, Zechstein Cycle 1, of the Sunderland district. It is confined to reef core and fore-reef talus slope facies and is absent from higher energy reef-crest and reef-flat habitats. Well preserved material permits the description of stereom microstructure and tooth construction. M. keyserlingi has teeth identical in structure to those of Recent cidarids and this contrasts with tooth structure in both the Carboniferous archaeocidarids and the early Jurassic euechinoids. Hemipyramid morphology and perignathic girdle structure also demonstrate the close relationship between M. keyserlingi and Recent cidaroids. Euechinoids and cidaroids must have diverged prior to the Upper Permian and at least two separate lineages of echinoids passed across the Permo-Triassic boundary.

Morphological constraint on egg size: a challenge to optimal egg size theory?

Some freshwater turtles appear unable to produce eggs large enough to achieve the balance between size and number of eggs predicted by optimal egg size theory. We present evidence that pelvic girdle structure constrains egg size and thus offspring size in females of smaller-bodied species (Chrysemys picta and Deirochelys reticularia). The constraint is demonstrated by the correspondence of slopes of the increase of the pelvic aperture and egg width with increasing body size. This constraint appears to be relaxed in a larger-bodied species (Pseudemys scripta), in which the increase in pelvic aperture relative to body size is greater than the increase in egg width. This type of structural constraint on a reproductive trait should not occur unless there is strong selection on pelvic architecture for other functions, such as locomotion, support, and limb retraction, that prevent expansion of the pelvic aperture. Although other explanations may exist for other groups of organisms that appear to vary egg size, the large variation in egg size associated with body size in some species of turtles can be reconciled with optimal egg size theory only if a pelvic constraint model is accepted.