Morphological innovation in Sulawesi ricefishes: The prerequisites of pelvic brooding
-
1
Zoological Research Museum Alexander Koenig (LG), Germany
-
2
University of Oldenburg, Germany
Evolutionary novelties can be driving forces shaping biodiversity. Studying the patterns and processes that give rise to them help to better understand how new character sets can arise. In novel reproductive strategies morphological, physiological and behavioral traits are often affected at the same time. Thus, studying novel traits allows to identify the interplay of multiple aspects that collectively contribute to an evolutionary innovation.
In Sulawesi ricefishes (Beloniformes: Adrianichthyidae), two lineages evolved a novel reproductive mode referred to as “pelvic brooding” (KOTTELAT, 1990; PARENTI, 2008; HERDER ET AL., 2012). In contrast to other ricefishes like the Medaka (Oryzias latipes), females of pelvic brooding species carry a fertilized egg-cluster in a ventral concavity until the fry hatches (YAMAMOTO, 1975; IWAMATSU, 2008). While elongated pelvic fins cover the eggs, attaching filaments connect the egg-cluster to the mother by forming a distinct plug structure, which is anchored inside the females’ ovarian cavity (IWAMATSU, 2008). The attachment of the egg-cluster delays ovulation, while an accidental loss of the eggs induces faster recurring oviposition (IWAMATSU, 2007). Moreover, the genital papilla, which lies in close proximity to the egg-cluster, appears more prominent in pelvic brooding than non-pelvic brooding females and is potentially connected to this specific brooding strategy. To this point, only a limited number of studies investigated this complex set of characters, addressing individual aspects of pelvic brooding (KOTTELAT, 1990; IWAMATSU ET AL., 2007, 2008; PARENTI, 2008). In order to better understand the morphological prerequisites of pelvic brooding, this study aims to compare multiple traits across seven Sulawesi ricefish species with regards to their brooding strategy.
By using high resolution µ-CT scanning, the bone morphology of both sexes was investigated, focusing on the thoracic body region and the pelvic fins. Additionally, specific soft-tissue scans were performed to shed light on the positioning of the aforementioned plug structure inside the ovarian cavity. The results show, that females of pelvic and non-pelvic brooding species are clearly distinct in pleural rip length. Furthermore, males and females of pelvic brooding species also differ in this respect. Three to four pleural ribs undergo a significant shortening exclusive to females of pelvic brooding species. This reduction in rib length appears to be the basis of the previously described ventral concavity, which likely forms one of the core prerequisites for pelvic brooding. Cut surface measurements of the pelvic fins also revealed that selected fin-rays are significantly thickened in pelvic brooding females compared to non-pelvic brooding females or conspecific males. This even holds true when correcting for total fin length, considering the elongated pelvic fins in pelvic brooding species. Preliminary soft tissue investigations of the plug structure in one of the pelvic brooding species (Oryzias eversi) show density differences across the plug structure. Thickened regions on the lateral parts of the plug close to the ovarian wall might contribute to a strong attachment and a tight fit in the urogenital canal.
Our findings support that “pelvic brooding” is a highly complex trait involving many morphological and physiological adaptations. Future studies will investigate the role of the genital papilla and whether behavioral adaptations accompany this special reproductive strategy.
References
1. Herder, F., Hadiaty, R. K. & Nolte, A. W. Pelvic-fin brooding in a new species of riverine ricefish (Atherinomorpha: Beloniformes: Adrianichthyidae) from Tana Toraja, Central Sulawesi, Indonesia. Raffles Bull. Zool. 60, 467–476 (2012).
2. Iwamatsu, T., Kobayashi, H., Sato, M. & Yamashita, M. Reproductive role of attaching filaments on the egg envelope in Xenopoecilus sarasinorum (Adrianichthidae, Teleostei). J. Morphol. 269, 745–750 (2008).
3. Iwamatsu, T. et al. Oviposition cycle in the oviparous fish Xenopoecilus sarasinorum. Zoolog. Sci. 24, 1122–1127 (2007).
4. Kottelat, M. Synopsis of the endangered Buntingi (Osteichthyes: Adranichtyidae and Oryziidae) of Lake Poso, Central Sulawesi, Indonesia, with a new reproductive guild and descriptions of three new species. Ichthyol. Explor. Freshwaters 1, 46–67 (1990).
5. Parenti, L. R. A phylogenetic analysis and taxonomic revision of ricefishes, Oryzias and relatives (Beloniformes, Adrianichthyidae). Zool. J. Linn. Soc. 154, 494–610 (2008).
6. Yamamoto, T. (1975). Medaka: (Killifish). Biology and strains. Series of stock culture in biological field. Keigaku Publishing Company.
Keywords:
Pelvic brooding,
Bone morphology,
Ricefishes,
Morphological innovation,
maternal care,
Reproductive system
Conference:
XVI European Congress of Ichthyology, Lausanne, Switzerland, 2 Sep - 6 Sep, 2019.
Presentation Type:
Oral
Topic:
MORPHOLOGY, ONTOGENY AND PALAEONTOLOGY
Citation:
Spanke
T,
Hilgers
L,
Wipfler
B,
Flury
J,
Nolte
AW,
Herder
F,
Misof
B and
Schwarzer
J
(2019). Morphological innovation in Sulawesi ricefishes: The prerequisites of pelvic brooding.
Front. Mar. Sci.
Conference Abstract:
XVI European Congress of Ichthyology.
doi: 10.3389/conf.fmars.2019.07.00075
Copyright:
The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers.
They are made available through the Frontiers publishing platform as a service to conference organizers and presenters.
The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated.
Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed.
For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions.
Received:
30 May 2019;
Published Online:
14 Aug 2019.
*
Correspondence:
Mr. Tobias Spanke, Zoological Research Museum Alexander Koenig (LG), Bonn, Germany, t.spanke@leibniz-zfmk.de