Miniature Species Research Articles

Tiwaripotamon keeae sp. nov. (Crustacea: Decapoda: Potamidae), a new miniature species of freshwater crab from the China-Vietnam border in Napo, Guangxi

A new miniature species of freshwater crab from the genus Tiwaripotamon Bott, 1970 (Potamidae), is described from a montane karst area in southern Napo, at the China-Vietnam border. It is the twelfth known species of the genus, and is also the smallest known, with the largest adult specimen observed barely exceeding 20 mm in carapace width. Apart from the small size, features of the eyes, carapace and ambulatory legs further set Tiwaripotamon keeae sp. nov. apart from its congeners. Pairwise genetic distances of the mitochondrial cytochrome oxidase subunit I (COI) gene also support it as a distinct species.

Digest: Are female miniature geckos larger than males?

What shapes the differences in body size between males and females in miniature species? One potential key factor is reproduction, which could constrain body size evolution because females of miniature species need to remain large enough to lay viable eggs. Glynne and Adams (2024) tested this hypothesis in two gecko families, the Sphaerodactylidae and Phyllodactylidae. Their findings support this hypothesis, indicating that female-biased size differences in miniature species are shaped by selection for reproductive success.

Label-free, whole-brain in vivo mapping in an adult vertebrate with third harmonic generation microscopy.

Comprehensive understanding of interconnected networks within the brain requires access to high resolution information within large field of views and over time. Currently, methods that enable mapping structural changes of the entire brain in vivo are extremely limited. Third harmonic generation (THG) can resolve myelinated structures, blood vessels, and cell bodies throughout the brain without the need for any exogenous labeling. Together with deep penetration of long wavelengths, this enables in vivo brain-mapping of large fractions of the brain in small animals and over time. Here, we demonstrate that THG microscopy allows non-invasive label-free mapping of the entire brain of an adult vertebrate, Danionella dracula, which is a miniature species of cyprinid fish. We show this capability in multiple brain regions and in particular the identification of major commissural fiber bundles in the midbrain and the hindbrain. These features provide readily discernable landmarks for navigation and identification of regional-specific neuronal groups and even single neurons during in vivo experiments. We further show how this label-free technique can easily be coupled with fluorescence microscopy and used as a comparative tool for studies of other species with similar body features to Danionella, such as zebrafish (Danio rerio) and tetras (Trochilocharax ornatus). This new evidence, building on previous studies, demonstrates how small size and relative transparency, combined with the unique capabilities of THG microscopy, can enable label-free access to the entire adult vertebrate brain.

Contrasting genetic and morphological differentiation among geographical lineages of a stenotopic miniature rasborine, Boraras maculatus, in Peninsular Malaysia.

The variability in the stenotopic miniature rasborine Boraras maculatus (Cypriniformes: Danionidae: Rasborinae) across acidic-water habitats of Peninsular Malaysia (PM) was investigated using two molecular markers (the mitochondrial cytochrome c oxidase subunit I [COI] gene and the nuclear rhodopsin gene), as well as morphological evidence. Molecular phylogenetic analyses revealed differentiation among populations of B. maculatus in PM with the distinction of four allopatric lineages. Each of them was recognized as a putative species by automatic species delimitation methods. These lineages diverged from each other between 7.4 and 1.9 million years ago. A principal component analysis (PCA) was conducted to examine the multivariate variation in 11 morphometric measurements among three of these lineages. PCA results showed a significant overlap in morphological characteristics among these lineages. Additionally, a photograph-based machine learning approach failed to fully differentiate these lineages, suggesting limited morphological differentiation. B. maculatus represents a case of morphological stasis in a stenotopic miniature species. Strong habitat preference, coupled with long-term habitat fragmentation, may explain why each lineage of B. maculatus has a restricted distribution and did not disperse to other regions within and outside of PM, despite ample possibilities when the Sunda shelf was emerged and drained by large paleodrainages for most of the past 7 million years. The conservation status of B. maculatus and its peat swamp habitats are discussed, and it is concluded that peat swamps comprise several evolutionary units. Each of these units is considered a conservation unit and deserves appropriate protection.

Two new miniature translucent catfish species of the rare genus Tridens (Siluriformes: Trichomycteridae) from the Madeira River basin, northern Brazil.

Two new miniature species of the trichomycterid genus Tridens are described from the Madeira River drainage, Acre and Rondônia States, Brazil. Until this work, Tridens was a monotypic genus composed solely of Tridens melanops, from the Putumayo/Içá River drainage, upper Amazonas River basin. Tridens vitreus sp.n. is known from upper and middle Madeira River drainage and differs from all other congeners by the lack of pelvic fins and girdle and by vertebra and dorsal-fin ray counts. Tridens chicomendesi sp.n. is known from Abunã River, middle Madeira River drainage and is distinguished from all other congeners by the number of vertebrae, dorsal-fin ray count and anal-fin base colouration pattern. Tr. chicomendesi sp.n. is further distinguished from T. vitreus by a combination of character states regarding the position of urogenital opening, dorsal-fin position, anal-fin position, maxillary barbel length, number of premaxillary teeth, number of dorsal-fin rays, number of anal-fin rays, number of lateral-line system pores, frontal bone anatomy, degree of ossification of maxilla, anatomy of quadrate-hyomandibular joint, size of posterodorsal process of hyomandibula, length of opercular patch of odontodes, number of interopercular odontodes, proportion of upper hypural plate cartilage relative to its area ; by the absence of a proximal, distal and ventral cartilages on ventral hypohyal; by the absence of a lateral process on basibranchial 4; by the presence of a cartilage block on the lateral process of autopalatine, the presence of a well-developed ossification on proximal margin of ventral hypohyal, the presence of hypobranchial foramen; and by the presence of an anterior cartilaginous joint between quadrate and base of posterodorsal process of hyomandibula. This work represents the first species description for the subfamily Tridentinae in more than 30 years and for the genus Tridens since its original description in 1889.

Unraveling Siren (Caudata: Sirenidae) systematics and description of a small, seepage specialist.

For approximately four decades, scientists have known of the existence of several undescribed species of Siren in the southeastern United States Coastal Plain. One of these species, S. reticulata, was recently described, but a small, seepage-dwelling species has remained undescribed until now. To resolve outstanding questions concerning the phylogeny of Siren, we collected sequence and morphometric data from specimens across the range of Siren. We found S. lacertina and S. reticulata to represent strongly supported monophyletic groups, with S. reticulata having a sister relationship to all other Siren. Additionally, we found five distinct mtDNA lineages within what has been recognized as S. intermedia. Siren lacertina and type-locality S. intermedia (lineage A) are sister mtDNA lineages, whereas S. intermedia lineages B and C show a high level of mitogenomic divergence from type-locality S. intermedia. Analyses of two scnDNA loci revealed that S. lacertina is monophyletic but nested with low positional support in a clade including the three S. intermedia mtDNA lineages. Further study is needed to determine whether S. intermedia lineages A, B, and C represent distinct species or incompletely sorted lineages. We restrict the range of S. intermedia to the region from the Escambia and Perdido river drainages of Florida and Alabama eastward through Virginia (the combined ranges of lineages A, B, and C). We also elevate S. i. nettingi (lineage E) to species status and include the larger S. i. texana form in that taxon, generating a species that occurs from the Mobile Bay drainages westward through the Mississippi Basin and southwest into northeastern Mexico. Lastly, we describe a new miniature species, S. sphagnicola, that ranges from the Florida Parishes of Louisiana eastward to the westernmost tributary creeks of Choctawhatchee Bay in the western Florida panhandle.

Small Body, Large Chromosomes: Centric Fusions Shaped the Karyotype of the Amazonian Miniature Fish Nannostomus anduzei (Characiformes, Lebiasinidae).

Miniature refers to species with extraordinarily small adult body size when adult and can be found within all major metazoan groups. It is considered that miniature species have experienced severe alteration of numerous morphological traits during evolution. For a variety of reasons, including severe labor concerns during collecting, chromosomal acquisition, and taxonomic issues, miniature fishes are neglected and understudied. Since some available studies indicate possible relationship between diploid chromosome number (2n) and body size in fishes, we aimed to study one of the smallest Neotropical fish Nannostomus anduzei (Teleostei, Characiformes, Lebiasinidae), using both conventional (Giemsa staining, C-banding) and molecular cytogenetic methods (FISH mapping of rDNAs, microsatellites, and telomeric sequences). Our research revealed that N. anduzei possesses one of the lowest diploid chromosome numbers (2n = 22) among teleost fishes, and its karyotype is entirely composed of large metacentric chromosomes. All chromosomes, except for pair number 11, showed an 18S rDNA signal in the pericentromeric region. 5S rDNA signals were detected in the pericentromeric regions of chromosome pair number 1 and 6, displaying synteny to 18S rDNA signals. Interstitial telomeric sites (ITS) were identified in the centromeric region of pairs 6 and 8, indicating that centric fusions played a significant role in karyotype evolution of studied species. Our study provides further evidence supporting the trend of diploid chromosome number reduction along with miniaturization of adult body size in fishes.

A new sexually dichromatic miniature Characidium (Characiformes: Crenuchidae) from the rio Guaporé, rio Madeira basin, Brazil, with remarkable morphological novelties to the genus

Abstract A new miniature species of Characidium is described from the midde rio Guaporé, rio Madeira basin, Rondônia, Brazil. The new species can be readily distinguished from all congeners by the sexual dichromatism, with females having narrow dark bars on body absent in males, and by the presence, in both sexes, of a black midventral dashed line extending from area between contralateral pectoral fins to at least the anal-fin origin. It can also be diagnosed from congeners by having strongly tricuspid teeth, with well developed and similar sized cusps in the premaxilla and outer series of dentary, and short lateral line with 6–8 perforated scales. Morphological novelties to Characidium observed in the new species include a rounded process on the first pleural rib near the vertebra, three or four haemal spines of the first caudal vertebrae distinctly elongate, neural and haemal spines of the antepenultimate vertebra not reaching origins of dorsal and ventral procurrent rays nor the origin of the caudal-fin rays.

A New Miniature Melocactus (Cactaceae) from Puerto Rico

A new species of Melocactus is described from Puerto Rico. This miniature species, with a stem no more than 70 mm in diameter, is of uncertain affiliation but is unlikely to be a close relative of M. intortus, the only other Melocactus known from Puerto Rico, due to the lack of a pink-coloured stigma, smaller stem dimensions and distinct seed structure. There are morphological similarities with some other Caribbean species: M. lemairei and M. praerupticola of Hispaniola, and M. guitartii (= M. curvispinus) from Cuba.

Cloning of FITM2 gene and investigating its expression levels in Banna miniature inbred pig (Sus scrofa) tissues

Fat storage-inducing transmembrane protein 2 (FITM2) plays an important role in regulating lipid storage and could be regarded as a candidate gene for intramuscular fat deposition in pigs. The aim of this study was to clone the coding domain sequence (CDS) of FITM2 gene, to compare the nucleotide acid and deduced amino acid sequences between breeds and species, to analyze the structure and characteristics of protein and to detect the expression profile of gene. The results exhibited that the CDS of FITM2 gene was 789 bp in length. The mutation of nucleotide acids led to the mutation of deduced amino acids between Banna miniature inbred pigs and other two breeds (Yorkshire × Landrace pigs and Duroc × (Landrace × Yorkshire) pigs). It was indicated that high identities of nucleotide acid and deduced amino acid sequences between Banna miniature inbred pigs and other species. The deduced amino acids were composed of loops and alpha helices in the structure. FITM2 protein may be a 30 kDa hydrophobic protein with 26 phosphorylation sites and one potential N-glycosylated site. FITM2 gene was widely expressed in various tissues, and the highest expression level was in adipose tissue.

Estimated richness and environmental correlates of miniature fish assemblages in the rio Jacundá, Brazil

Abstract South America is home to more miniature fishes (<26 mm in standard length) than any other continent. Despite this diversity, the ecology of miniature fishes is poorly studied. To promote the study of miniature fish ecology, we investigated patterns in total richness, assemblage structure and environmental correlates for miniature fishes in the rio Jacundá drainage of the Lower Amazon River basin, Pará State. Based on multi-pass dip-netting of leaf litter at 20 locations distributed across two sites, we collected miniature species and used rarefaction to estimate 9 to 14 species might be present. The miniature fish assemblage at the upstream site was a nested subset of the downstream site, and water pH and canopy cover, two features known to be altered by deforestation, correlated most strongly with assemblage variation. Our work represents one of the first quantitative assessments of environmental correlates with miniature fish assemblages and highlights research topics that should be investigated further to promote conservation and preservation of the overlooked and understudied Amazonian diminutive freshwater fish fauna.

Shrunken Life: Discourses of the Cryptic and the Miniature in Madagascar

As scientists scour remnant habitats and “unmask” cryptic species with DNA barcoding, a boom of species discovery has enchanted the world. In Madagascar, recent discoveries of previously unknown miniature frogs, chameleons, and lemurs often photographed on human fingers or cradled in hands, have captured the public imagination. In this imagery of scale, the giant finger conveys the outsized impact of humanity on Earth, or points to what Susan Stewart (1996, p. 74) calls “a physical world of disorder and disproportion.” Although the phenomenon of insular gigantism and dwarfism has shaped scientific discourses of evolution and extinction since the nineteenth century, recent reportage on “new” miniature and cryptic species reflects a sensibility beyond wistful nostalgia for creatures past. Species miniaturism evolves out of habitat loss, and living minifauna encapsulate the contraction of existential time, all the more pronounced by the effects of climate change. Photographs of cryptic minifauna therefore compel us to reflect on the whole of our losses, while they fuel the impulse to restock the “library of life” at micro-scale.

Description of two new miniature species of Hylopanchax Poll & Lambert, 1965 (Cyprinodontiformes: Procatopodidae), from northeastern Gabon, with an updated diagnosis of the genus based on morphology, colouration and osteology.

Two new species of the lampeye genus Hylopanchax are described from the Ivindo River basin in the Ogowe River drainage. Hylopanchax multisquamatus, new species, and Hylopanchax thysi, new species, differ from congeners by the presence of a hyaline urogenital male papilla with small black spots and a dark-brown reticulate pattern on the flanks of both males and females in preserved specimens. Hylopanchax multisquamatus is distinguished from congeners by the number of scales on the mid-longitudinal series (27-30 vs. 19-26, respectively) and by the relative anterior/posterior flank scale depth ratio (140%-150% vs. 170%-220%). Hylopanchax thysi is distinguished from all other congeners, except Hylopanchax paucisquamatus, by the presence of vertebrae (30 vs. 31-33) and is further distinguished from H. multisquamatus by the presence of a deeper caudal peduncle and much larger anterior flank scales. It is distinguished from H. paucisquamatus by the presence of a hyaline urogenital male papilla with small black spots and a dark-brown reticulate pattern on the flanks of both males and females in preserved specimens. Osteological data of Hylopanchax are presented for the first time, and an updated diagnosis based on external morphology, colouration pattern and osteology is provided. An osteological comparison with closely related species belonging to the genera Procatopus, Hypsopanchax and "Hypsopanchax" is presented. (a) A truncate and slightly downward-directed anterior process of the angulo-articular and (b) a guitar-shaped lachrymal with both its anterior and posterior margins sharply curved are here considered as diagnostic features of Hylopanchax.

Diversity in Pacific Slender-Toed Geckos, Nactus pelagicus Complex (Reptilia: Squamata), of New Guinea and Adjacent Islands

The diversity within the genus Nactus is slight in comparison to the other Australasian genus of narrow-toed geckos (Cyrtodactylus). The latter now has more than 290 species, with over half of these species newly described in the twenty-first century. In contrast, prior to this study, 12 Nactus species were recognized formally in the recent herpetological literature: three species in the Mascarene Islands, two in the Pacific Islands, three in Australia, and six in New Guinea and associated island groups. Three of these New Guinea species are miniature (snout–vent length ≤ 40 mm) species, and three are in the pelagicus complex; with the exception of the recently described N. kunan, all other New Guinean populations were labeled N. pelagicus even though they were known to be bisexual species and differed from the unisexual N. pelagicus of Oceania. Considering only bisexual New Guinean “pelagicus,” my morphological analyses recognize 24 distinct populations for which I provide new names or resurrected species names from synonymies. Of these 24, two species are extralimital (Morotai and Kei Islands). The sampling of Nactus in Indonesia Papua is very poor, with only one specimen from the base of the Vogelkop, two from south coast drainages, and more than a dozen from islands from the east coast of Cenderawasih Bay; the remainder derive from Papua New Guinea (PNG). The Indonesia Papua populations represent four species, two of which are shared with PNG. Papua New Guinea thus has a total of 20 species, varying from widespread species (e.g., north coast of main Papua to the Sepik-Ramu area) to a single locality in Madang or single islands in the Louisiade Archipelago. Most distributions of the PNG species match at least one other PNG anuran or reptile species. The greatest diversity of PNG species occurs in Madang Province to Huon Peninsula and the Milne Bay mainland with sympatry in both areas. The “pelagicus complex” of species is herein confirmed to be polyphyletic. In spite of its use in this study, its subsequent use should be restricted to the unisexual species and their parental species, of which only one (N. multicarinatus) is known. The preceding represents a subgroup within the larger clade of Australian and New Guinean bisexual species. For the present, I do not recommend a name for this group because a molecular phylogenetic analysis will be required to identify the cladogenesis of the Nactus species.

Miniaturization, Genome Size, and Biological Size in a Diverse Clade of Salamanders

AbstractGenome size (C-value) can affect organismal traits across levels of biological organization from tissue complexity to metabolism. Neotropical salamanders show wide variation in genome and body sizes, including several clades with miniature species. Because miniaturization imposes strong constraints on morphology and development and because genome size is strongly correlated with cell size, we hypothesize that body size has played an important role in the evolution of genome size in bolitoglossine salamanders. If this hypothesis is correct, then genome size and body size should be correlated in this group. Using Feulgen image analysis densitometry, we estimated genome sizes for 60 species of Neotropical salamanders. We also estimated the "biological size" of species by comparing genome size and physical body sizes in a phylogenetic context. We found a significant correlation between C-value and physical body size using optimal regression with an Ornstein-Uhlenbeck model and report the smallest salamander genome found to date. Our index of biological size showed that some salamanders with large physical body size have smaller biological body size than some miniature species and that several clades demonstrate patterns of increased or decreased biological size compared with their physical size. Our results suggest a causal relationship between physical body size and genome size and show the importance of considering the impact of both on the biological size of organisms. Indeed, biological size may be a more appropriate measure than physical size when considering phenotypic consequences of genome size evolution in many groups.

Two new miniature silverside fishes of the genus Membras Bonaparte(Atheriniformes, Atherinopsidae) from the Tropical North Atlantic Ocean.

Two new species of miniature silverside fishes are described from coastal habitats in the tropical Atlantic: Membras pygmaea sp. nov., from Brus Lagoon, Honduras, and M. procera sp. nov., from the Gulf of Urabá, Colombia. These new species belong to the martinica species-group within the genus Membras Bonaparte. The monophyletic martinica species-group (see below) contains four additional species, all coastal, marine that extend from the east coast of North America to São Paolo State, Brazil. Within the martinica species-group, all but M. martinica are miniature species, ranging from 41-60 mm SL. The smallest species, M. pygmaea sp. nov., is mature at 24 mm SL. A geometric morphometric analysis shows: (i) each species of the martinica species-group occupies its own portion of shape space; and (ii) none of the miniature species possess the shapes of small immature M. martinica. While some of the literature suggests that miniaturization may involve paedomorphosis, our results show that the miniatures accelerate to adult body forms.

On a remarkable sexual dimorphic trait in the Characiformes related to the olfactory organ and description of a new miniature species of Tyttobrycon Géry (Characiformes: Characidae).

Among the order Characiformes, secondary sexual dimorphism is commonly associated to the occurrence of bony hooks on fins, shape and length of the dorsal and anal fins, and sexual dichromatism. The analysis of a new miniature Characidae species of the genus Tyttobrycon, described herein, yielded to the discovery of a sexually dimorphic trait related to nostril aperture and number of olfactory lamellae. In this type of dimorphism, mature males present larger nostril aperture and higher number of olfactory lamella than females. A dimorphic olfactory organ is for the first time recorded and described for a member of the Characiformes. Gross morphology and development of brain and peripheral olfactory organ of Tyttobrycon sp. n. are described and compared to other species of Characidae. It is hypothesized that such dimorphic trait is related to male-male detection during cohort competition in small characids. The new species of Tyttobrycon is diagnosed from its congeners by the number of branched anal-fin rays (19–21) and the absence of a caudal-peduncle blotch. It occurs in a small tributary of Rio Madeira basin, near to the limit between Brazil and Bolivia, Acre State, Brazil.

A new species of miniature Characidium (Characiformes: Crenuchidae) from the upper Rio Paraguay basin, Mato Grosso state, Brazil.

A new miniature species of Characidium is described from the upper Rio Paraguay basin, Brazil. The new species can be diagnosed from all congeners by the presence of a dark-brown humeral blotch, vertically elongated (spanning 5 to 7 horizontal scale rows), with the shape of an upside-down acute triangle. Additionally, it can be diagnosed by a short lateral line (6 to 8 perforated scales), the absence of a conspicuous peduncular blotch, a lower number of principal caudal-fin rays (14-16) and by absence of the adipose fin. The new species is the smallest species of the genus; the largest specimen was 19.3 mm standard length.

An analysis of maximum body size and designation of size categories for notothenioid fishes

There has been no comprehensive study of body size in notothenioid fishes. Therefore I evaluated maximum total length (TL) as an axis of the evolutionary radiation. Lengths are provided for 141 species that collectively range in maximum adult size from 5.7 cm (Harpagifer nybelini) to 225 cm (Dissostichus eleginoides), a 39-fold difference. For the 138 species analyzed, the mean length is 33.5 cm and the median is 26.6 cm. Based on 10 cm-bins, notothenioids are apportioned into small ( 200 cm) size categories. The 20–29 cm bin contains the most species (32%). Most species (71%) are of medium size, 21% of species are medium-large, and 7% and ≈ 1% are small and large, respectively. The median lengths vary among the five cryonotothenioid families as well as among eight clades (genera and families). Among families, median and mean lengths are smallest in the Harpagiferidae and largest in Channichthyidae. Among clades, Harpagifer has the smallest median length (8.3 cm) followed by Artedidraco (12.5 cm). Several middle-sized clades do not differ in median size: Patagonotothen, Trematomus, Pogonophryne, and Bathydraconidae. Two clades of medium-large size species, Notothenia and Channichthyidae, are of similar size. A significant but weak positive relationship exists between maximum length and maximum depth. With the exception of miniature species ( ≤ 1 cm), the 126 species of cryonotothenioids (the Antarctic clade) encompass the range in size categories in actinopterygians in general, and the disparity in maximum lengths among individual species indicates that body size is an axis of the radiation. I discuss the size of notothenioids relative to other teleosts, the ecological implications of large species in the food web, and the similarity of the cryonotothenioid axes of diversification to those of Lake Baikal sculpins.

Dario kajal Britz & Kullander, 2013 (Percomorpha, Badidae): the first documentation of the genus Dario Kullander & Britz, 2002 from Bangladesh

We document for the first time in Bangaldesh Dario kajal Britz & Kullander, 2013, a little-known miniature badid species originally described from the Jaintia Hills, India. We provide records of 8 specimens from 3 localities, of which, 2 are in the Meghna basin. Our finding also confirms its distribution from the Brahmaputra drainage, about 300 km southwest from the type locality. The genus Dario Kullander & Britz, 2002 was previously unknown from Bangladesh.